In Assassin’s Creed: Brotherhood for the PS3, Xbox 360, and PC, you can unlock several different guild crests for your character to represent.
Assassin’s Guild Crest – Complete all Assassin’s Guild challenges
Courtesan’s Guild Crest – Level up each guild to level two
Mercenaries Guild Crest – Level up each guild to level two
Thieves Guild Crest – Level up each guild to level two
Check out my other guide for a full list of unlockable guild rewards.