In Assassin’s Creed: Brotherhood for the PS3, Xbox 360, and PC, you can unlock some Knife Belt upgrades for your character.
There are two upgrades you can receive for your Knife Belt. The first one unlocks when you open four Tailor shops in the Rebuilding Rome mini-game. The second one unlocks when you open eight Tailor shops.
Check out my other guide for more unlockables from the Rebuilding Rome mini-game.