The Sonic Stadium has a prototype article.
Apparently, the clothing maker "Insert Coin" will be producing a series of items including
Green hill all-over design leggings for girls
Tees & Sweatshirts for anyone to wear
Everything OTHER than the leggings seems to be of a subtile nature. There's nothing with a picture of a character on it. The article is here on prototypes because they don't have any actual photos of real clothing, it's all just drawings of stuff with the design pasted on there. Use the link to see:
Knuckles Gym hoodie, Project Shadow, Sonic snakers tee, Miles Prower shirt with tail-like logo, South Island shirt with super fine print on it. While the shoes are instantly recognizable, it'd take a real Sonic fan to identify the Project Shadow logo, or catch onto the "Knuckles Gym". Interesting to see a whole line going with the 'very subtle Sonic' angle. The items will appear around SonicGear once physical photos are released.