If there is a way to find out what the 'real' name is, then this whole system will be useless. Then you won't just let Bob inside, but you will look at the main account name of Bob before you let him in.
Maybe we should just drop the idea of names altogether and instead use a character generator where you can randomly generate a character until you find one appealing and use that as permanent character. Would need a lot of character details though, so that it should be possible to always see the difference between two men. And you'll also always be able to reset this, at the expense that your character will die and no one will remember you.
This together with some system where you as player can custom make an item such as an arm bandage thing with it's own color and logo (Or perhaps even a 'paper' which is basically a picture which you can show), should help with saying: Oh I'm with this group
I'd almost say, be able to connect colours or names to players yourselves, but then it'll be impossible for a stranger to get inside (It will probably make life a lot easier)
Edit: Perhaps a nametag that people can read?
^
i gotta say this idea is really really intresting :O
no nametags at all? yes please! but that means you have to get either a completely random looking character (appearance wise etc) so everyone is actually clearly distinct from one another. add in scars etc and facial hair and tada.
and when you log in you see your own character from the front for a couple of seconds so you know what you look like =)