These twenty-five artifacts explain America (gifted link)

My little list...

Twelve-lane highways
Domed stadiums
Silicone breast implants
Landfills turned into ski hills
Press-on nails
Mickey Mouse watches
Corn dogs
Jeeps
The oblate spheroid version of football
Blue jeans (especially "designer")
The Big Gulp soft drink size

I'll think of more later.

Very interesting, thanks for the share. I have some things to add, just from my time living abroad. Some of them are things people pointed out to me, some of them are things I noticed myself. Most of them feel food related.

• PB&J sandwiches. Sandwiches are ubiquitous worldwide, everyone has one. But I think the PB&J sandwich is uniquely American. Almost all of us (without nut allergies) have had one growing up at some point. And as an adult, they still hit the spot.
• Cheese wiz. This is what many Europeans think of when they think of artificial cheese food products. Some of them have told me they think this is the only cheese Americans eat. I would also say it is a great example of our long experiment in the industrialization and creation of food in a lab.
• Chocolate Chip Cookies. A classic. Most countries have a sweet of choice when they're out at a cafe, or getting a sweet treat, and in the US it's often a cookie. Had to go with chocolate chip, both because it was invented in the US, and is a common favorite.
• Yellow school busses. I don't know why, but for some reason this is one of the things I get asked about most. Have I ridden one? Are they really that common? (Yes and yes). School busses exist in many countries, but few of them look like ours.
• A gun. I feel like this one really doesn't need explanation.
• Branded sports team athletic wear. I hadn't really thought of this as American until I moved abroad, but we apparently have a unique way of designing and branding our sports teams. A lot of people outside the US think it looks really cool, and I commonly see non-Americans wearing clothing and hats for teams they don't even know the name of, they just like the outfit.
• Diner napkin dispensers. This one is multilayered for me. For one, diners don't really seem to exist outside the states, at least in Europe. I've been to diner-themed restaurants run by Europeans, but there's always something about them that still makes them feel like a restaurant with diner theming, not an actual diner. Two, in the US, napkins are usually placed somewhere easily accessible by visitors, who are encouraged to take as much as they want. Kind of an example of how customer service works there. In Europe, napkins are usually kept with the cashier or somewhere in the back of house, and are distributed to customers in small amounts. They will of course give you more if you ask, but you must ask. Just a difference in philosophies I've noticed, perhaps an example of American excess.
• Interstate signs. Another uniquely American design (how it looks, that is), and an example of our car culture. Really common to see pictures of random interstate signs in American-themed restaurants. It always makes me laugh, as it feels so random to me.
• An American football helmet. Representative of the sport, the violence common in our media, how we try to market ourselves internationally (and how sometimes it doesn't work the way we think), and our bandaid attempts to help the people impacted by the violence.
• Garlic powder. An ingredient that doesn't seem to be very common in European recipes that I've found, but an integral part of many American regional cuisines, including BBQ, cajun, Italian-American, and many others. Some of the Europeans I've talked to think that we use it instead of garlic, and while I'm sure there are people who use it that way, it is more a separate spice that is meant to provide flavor in addition to or separately. Most commonly used in rubs, marinades, soups, stews, and sauces.
• Thanksgiving hand turkey drawings. Another thing most of us did as kids. Don't know of anyplace else that does them. Maybe in Canada for their Thanksgiving?
• Green-dyed beer. American St. Patrick's Day celebrations are slowly being exported back to the UK. A bit awkwardly, actually, as the English totally don't really consider how the Irish might feel about their shared past and just enjoy the fun American-style drinking. But yes, this is an American style of celebration, St. Patrick's Day isn't really a big thing in Ireland, and Corned Beef is also only an Irish American tradition.
• Jack-o-lanterns. Halloween comes from a Celtic tradition, and was probably started in Canada, but internationally is seen as an American holiday. They don't seem to do a lot of trick or treating (though I hear some neighborhoods do), but costume parties are fairly popular. I've not really seen a lot of jack-o-lanterns here, and still feel like that's only really common in the US/Canada.

To be honest I'll probably think of more. It's a fun question, and there are many things I've noticed over the years.

Had so much fun coming up with my list of items for the states, decided I also want to come up with a list for my current home, England. This list is made with affection (and some criticism), and from the outside perspective of an American who only moved here as an adult. In no particular order, but numbered so that I can keep track of 25 items:

1. A ploughman sandwich. A simple sandwich consisting of cheese and pickles on bread. Sometimes adds ham if you're getting fancy. This is actually a really old lunch, going back centuries, and was the lunch of farm workers. England has an interesting history in that before the industrial revolution, they were invaded and conquered often enough that much of the food they are famous for today was from the invading cultures. And once they became a large empire, taken from other cultures. Even the famous fish and chips are from Jewish immigrants. But this one is 100% original to the isles. It reminds me of a good PB&J in it's simplicity but brilliance. A nice salty, sharp cheddar matches with sweet, tangy, and sour pickles. Putting in the effort to find good ingredients for the sandwich results in one of my favorite sandwiches I've ever had.
2. Cake. If cookies make me think of America, cake makes me think of England. Very common and popular, often seen in cafes as something to get as a quick afternoon treat.
3. Electric kettles. There are coffee countries and tea countries, and England is famously a tea country. When I moved here, I expected tea rooms to be a more popular thing then they are, but they seem to be more of a tourist activity. Instead, tea seems to primarily be a drink that's taken at home, or perhaps in the office as a pick-me up. If you're grabbing a non-alcoholic drink in public with friends, coffee shops and cafes are still more popular. So everyone needs an electric kettle! Tea time at home or in the office is a much more low-key affair then I imagined, but still quite pleasant. Make yourself a cuppa, and have it with a biscuit.
4. Double-decker buses. Much like a yellow school bus, I had to put this one. Was so excited to ride them when I moved here. If you're visiting any UK city and are trying to learn the sights, I highly recommend looking up a bus route that loops through the city center, and just sitting on the upper level of one. It's a low cost way to see things, the view is fantastic, and it's a good way to rest your feet.
5. Tunnock's tea cakes. I suspect this may be a controversial choice for any UK readers, but let me explain. These sweets have the reputation in the UK of being a sweet your grandmother keeps in the house. But for everyone else from other countries I've introduced these cakes to, they go wild for them (including myself). For those unfamiliar, they are a large mound of marshmallow fluff on top of a shortbread biscuit and encased in chocolate. I'm also somewhat cheating because this is a Scottish brand, but it is an English tradition to claim it as their own. But to my overall point, in general the sweets me and my international friends tend to enjoy the most and find interesting are usually older, more traditional ones. I think in an age of globalization, these sweets are unique and have not typically been encountered previously. Kit kats and skittles are available globally and tailored to local tastes, but Tunnock's tea cakes, or flying saucers (another favorite of mine) are not. I even got to experience the same thing in reverse, when a friend returned from a visit to the US. He had brought back a large bag of tootsie rolls, a candy there that I associate with my Grandpa and find kind of old fashioned. Everyone from the UK he gave them too absolutely loved them, which surprised me, but at this point probably shouldn't.
6. Fox poo shampoo. Foxes are everywhere in the UK, including the cities. They basically play a similar role to raccoons in the US, often scavenging from rubbish bins and getting into cute/frustrating shenanigans. They are also, similar to raccoons, in the early stages of domestication. Their shit must smell absolutely amazing to my dog, because she insists on rolling in it every time she finds a fresh one. Was amused to find out that it's apparently a common enough problem for dog owners, that specific shampoo exists for it. I also like this as a representation of UK dog culture in general. This country is a leader in dog behavioral research, and dogs are very popular pets here. A great place to have a dog, aside from the shit rolling.
7. Shredded, stale bread. The UK, like many Western countries, has a mixed record on environmentalism. I've thought they were doing well at switching over to green energy sources even before the Ukraine war, and many people here do try very hard to conserve electricity and water. But when it comes to nature conservation, I feel there is a blind spot. It is not uncommon for people to walk their dogs off leash in their national parks, with no thoughts about the dogs disrupting the wild animals living there. Cats famously spend most of their days outdoors here and are actively hunting a native bird population that is already impacted by habitat reduction and other invasive species. Most of the trees that were once on the island have been cut down, a real shame because many of the forests that used to exist here would qualify as the rare, temperate rainforest. Grazing livestock are allowed free roam, unfortunately making it difficult for the forests to recover, as many of them like to eat young saplings. Where does the stale bread come in? It is very common to see people leave it on the ground to feed birds in parks. Some of these people likely mean well, but bread is notoriously unhealthy for wild birds as a diet, and again disrupts the local wildlife. I do think it is rare here to find places that are untouched by humans, and perhaps because of that people have a hard time in seeing how their actions impacts the nature around them. What I find frustrating when I ask people here about this, is that they just seem to shrug their shoulders and say it's always been this way, the wildlife is used to it. No, I say it hasn't (most of the tree reduction in the UK happened in the 20th century), and also, it can change.
8. Cask ales. A style of beer that is completely unique to the UK. It's unique in that it continues to ferment after the primary fermentation at the brewery, up until the moment it is hand-pulled into the pint. It's unfortunately a style of brewing that might be in trouble. IPAs have taken over as the most popular beer at the moment, and the unique properties of cask ales make them unattractive to pub and bar owners when compared to beers kept in kegs. Cask ales must be consumed quickly once tapped, as they will go bad within days (a hard sell if the place isn't moving high volumes of them), compared to the weeks shelf-life of kegs. They require unique infrastructure to hand pull them. And the beer is served warmer than kegged beer, which can make it unattractive to customers. They are delightful though, and I recommend them to anyone who's curious to try them.
9. Model trains. Trains are to English history, what the plane is to US history. The invention of them was a significant factor in the development of the British Empire, and they still see high use today. People who are really into trains here are, really into them. Model trains are often popular among train fans, and I've seen some really elaborate displays. The National Rail Museum in York has an extensive model train setup, as well as a very cool collection of train engines and anything relating to trains. As a side note, a lot of the older train stations here are gorgeous, with really beautiful iron work. Worth visiting some of them even if you don't ride a train.
10. Artificial turf. England loves gardening, and has a style of doing so that is very, orderly? People seem to love lawns, and people will often criticize gardens that they think look disorganized (including ones that are purposely being left to meadow). Artificial turf seems oddly attractive to people for this reason. It always looks green, requires no maintenance or sunlight, and looks kinda like a lawn (from a distance). A real one is better of course, if you can afford it.

Wow, this grew much longer than I anticipated. Gonna take a break for a bit, then come back to do the next round.