as I said, ego-boosting. Plus, I am an ordinary citizen-yes I have held some 'prominent' positions, but I define myself by myself, not by my office
Some people even put "So and so Candidate" in...now that really shows off a worryingly low sense of self-esteem.
But now that I finally hold an elective position, I've put it in too...
Or some folks put in positions in their title that have no relevance or official duties at all.
Putting in "Senator" is helpful, however. When the Senate is casting its votes and debating, it makes it easier to identify who is speaking and voting from an official capacity, and who is merely an interested observer.