It's the norm in academia to put your educational or career level after your name in your email signature, but only in email. Instructors sign with "Their Name, Associate Professor," "Their Name, Distinguished Professor," or such. They don't need to include Ph.D after their name because it's assumed that any professor at a Research 1 university has a Ph.D. Grad students follow their name with "Doctoral Student, subject area" until they get their master's and then they add "M.A." before that. I'm one of the few students who has not put my educational level in my signature because I just can't get over feeling pretentious about it. But I plan to go into teaching when I'm done, so once I start looking for a position I'll have to add the Ph.D. to my name. No one ever uses these titles outside of email sigs though. That's beyond humble-bragging, that's downright obnoxious.
This thread makes me think of the Andy Griffith Show (anyone remember this or watch the reruns?), where Barney Fife signs his name with M.D. after it. When Andy questions this Barney says it stands for Mayberry Deputy.