I run into this sometimes (but not often) in my professional life. Instead of signing off their email with their full name, or first name, they simply put the first letter of their name.
Example of ending of email :
I'm trying to sense if I'm off base with this, but I find it pompous. To me, it suggests the sender believes they hold a position of importance. They claim a single letter as their own, ahead of everyone else. Or it suggests the sender believes they are so busy/productive, they choose to save time by not spelling out their full name. Pah.