Just seen this on the main Forza forum.
You can get a free Avatar T-Shirt with "I AM THE STIG" on it.
https://apps.facebook.com/xboxforzatopgear/uk/
There are user on the main Forza forum saying thein the US and got it.
I have just done it, it ask for your GamerTag before giving out the code, which I redeem via xbox.com but you should be able to use it via the Xbox 360.
You can get a free Avatar T-Shirt with "I AM THE STIG" on it.
https://apps.facebook.com/xboxforzatopgear/uk/
There are user on the main Forza forum saying thein the US and got it.
I have just done it, it ask for your GamerTag before giving out the code, which I redeem via xbox.com but you should be able to use it via the Xbox 360.