We don't use GM Sprites on our server, so Staffers are identified by a Staff-Only "Solstice-Wing" to differentiate. They're untradable, and GMs are monitored closely, are only allowed to have ONE GM character(any other instances will be deleted) to prevent confusion.
A posting of the Staff List is a must on any server's forum or Rules so players know exactly who to look for. The case on Solstice is that none of my GMs talk like twits, so any impersonation would be easy to catch, since 90% of the impersonators are illiterate and can't communicate clearly, such as in cheesestix's example. There has only been one impersonator, and he or she made a BIG mistake PMing my Admin, assuming it was a normal player with...
solstice-GM : hay player u wan donation item?
Descent : Are you giving them away?
solstice-GM : ya
solstice-GM : i am owner of this serv
Descent : Really.
solstice-GM : ya i am owner of this serv
Descent : How exciting! You're taking time out to talk to me?
solstice-GM : giv acct plis
solstice-GM : n i giv donation item
Descent : Okay, write this down.
solstice-GM : ok
Descent : My account info is as follows...
solstice-GM : ok
Descent : Username : Your donkey
solstice-GM : ok
Descent : Password: Is Banned.
solstice-GM : ei
Descent : Bye bye. @ban 999d
Jumped into the files to IP ban the little turd. Haven't seen him since. What was humorous was that I had a few players hanging out in Prontera to watch this, laughing up a storm as the 1/1 Novice attempted to tell people he owned the server.
I'm sorry, but this made me laugh...
I did too.
There was a kid who tried this with me before, except the admin was my friend.
I just so happened to be over at his house.

So he and I got the chance to toy with this guy, gave him a 1/1 novice account, he logged in and was like, ei why dun u hav ny itams, r u new?
Re: Hmm, neither do you, as I can see you just made the account you are on, and you have another account by the name of xxkamo***xx
his re: wahhh?
Re: oh yes, I forgot to tell you, I am quite close friends with the owner and admin of this server...I just so happen to be sitting right next to him ^^
*scammer logs out*
*ip bans permanently*
Ahhh, I love it when people try to impersonate GMs.
They are so entertaining. I hope I have a few on my server once I open to the public.