Gears of War 3 - The unlockable rewards for the avatar.
Design your avatar from Gears.
In Gears of War 3 you can unlock some nice items to wear to your avatar by completing particular objectives, here are these prizes and what you need to do to unlock them:
Horde T-Shirt: unlock the "Welcome to Horde Mode" achievement
Locust Drone Mask: unlock the "Welcome to Beast Mode" achievement
Marcus' doo-rag: complete the campaign on any difficulty