Mine (Ghost) is due to the tongue-in-cheek running joke that I can be whoever I want in the hobby or the forums at any given time and...
my belief that constant monitoring and tracking of individuals in the hobby has impeded innocent people more than the "bad people"
an attempted constant reminder that almost everyone in the hobby presents who they want to say they are but are likely, truly (on perhaps some insecure level) not that person (everyone presents an idealized version of self to strangers)
that the shocking twist of this community is that there are a lot of "people playing characters who play characters" and I, myself, could literally be a convicted 4x felon and the only way anyone would know it is if I gave them actual personally identifying information to reveal that to them.
Not trying to provoke, but this is literally why I go as Ghost here. On an internet anonymous text-based, non-video/voice hobby...we are whoever the fuck we tell you we are until figured out otherwise.
-edit:
I actually just recently got a discord ping from a MUer I hadn't talked to in maybe 3 years. I don't even remember truly who they were but I could read our chat history in back-scroll about MU. They tried to get me to download a piece of software that was clearly malicious, and I thought:
Did they get hacked?
Is it the same person, but they're trying to scam me?
Did they (as an actual MUer) send me a link to a website or game hoping to determine my IP to try to lock me out of some MU or prove I wasn't on some game?
I realized from what I've seen over the years, all 3 were realistic possibilities so I reported the person and blocked them. So feel free to use "Ghost" as much as you want or whatever, there really are no guarantees
(Also: I don't think I ever repeated charnames so can't answer 2nd)