I think we could start a new trend to make the world better by trading advertisement for tips and how to behave in a society. The important thing is not to be invasive or change the user experience in any way.
So do you see the top bar where we don't have nothing? I think it would be a great place to have a new phrase on every refresh like this:
"A bottle of plastic is to put in the yellow trash can".
"Open Source is important so we don't rely on company's for everything"
"If you smoke please don't throw butts in to the ground, buy a cheap portable ashtray"
"Remember that not everyone is having good day"
"Don't throw cotton swab in to the toilet"
"When brushing your teeth turn of the water in the dead times or better use a cup to use less water"
"2OATH is always important to have"
"Password manager is a must have now a days (having the same password in everything defeats the purpose)"
"Read more than the titles before you make conclusions"
"When driving don't forget to use the lights when turning/changing lanes"
"Think twice when using paper"
"Beverages are not water"
"Focus a distant point from time to time if you are long hours in front of the monitor)"
"When you are putting music in public you are invading the other space"
"Wait for the people to exit the train before entering"
"If you drink don't drive not because of you but because of the other people"
"Put the phone down while driving, everyone says that can do that before hitting someone"
Before of witch phrase it would say the topic.
I think for this phrases we can't have nothing political, religious or other topics that could change people views or that could offend.
Maybe we could have topics for country's because of the costumes.
Little things like this, I hope I could express the idea(more directs and simple maybe?). And if this is welcome maybe the correct way of doing this is making a repository on gitlab(every file would be a topic maybe) so everyone could add new phrases and use the list for other sites. Of course we would need to get a few trust worthy people that have a good sense of witch phrases to accept or create rules for them.
Maybe there is a better way of creating a public DB but I don't know any at least.
And if people wanted could select the topics they wanted(all or some or none).
This could also show the importance of donating and support open projects so we don't need to get money from third party's in any way and better yet, use the empty space to make the world a better place.