This nicely detailed tee was a pre-order bonus for the original Sonic Riders in 2006. If you pre-ordered from Sega, you would get this shirt in the mail later on. It's thought that all of them are mega XXL sized. The front has the Riders styled Sonic graphic, complete with 'line screen' sort of odd style shading for half of him.
The back has the 15th Anniversary logo (see inset, left) as well as the Riders logo in the bottom corner. For a bonus item, this is a nicely detailed shirt. Oddly, there is no official Sega tag on it. The cloth tag in the collar just says "Hanes Beefy T" with beefy bull logo...and they're just who made (the base shirt--it was then modified/design added by Sega). It is unknown why Sega didn't get a real tag for this. This shirt is in the SonicGear collection.