Anthony, if you're talking about the Guild of Thieves, it's not so secret that you can't ever ever talk about it. Especially OOCly on an external forum that I don't even have any control over, lol. I admire your willingness to not go into detail through.
What you're going to want to do is find an existing member. There's like 3 of them that are semi-active right now, one in particular plays quite a bit, daily. The Guild is entirely player-initiated. Just have one of them vouch for you and you're in.
Though, a good thief doesn't get caught. You might want to tone it down a bit. If your character gets a reputation of overt crimes and constantly being in jail, then that's actually going to work against you. the Guild doesn't want it's members revealing themselves to the public. A thief with a reputation is no good to them.
If you're talking about the Claw of Star, there's no restrictions to join, you just need to find the right NPC...
Lead Developer for CLOK