On the dashboard look for a cars land advertisement. You have to click all five red dots and see each one. Then it unlocks the avatar shirt. Don't know if it's US only.
Wanting to let everyone know there is a new xbox kinect fun labs game called Junk Fu to download in the marketplace. Its free as of now.
http://marketplace.xbox.com/en-US/Product/Junk-Fu/7d75e76f-d2a5-42ee-b579-69cec081a62a?cid=SLink