It's not always possible from just the cart - some US games have the purple stripe down the side, some PAL carts have -50 at the end of the 670-xxxx product code and the type-face used for 'Game Gear' on the cart can sometimes give it away aswell.Originally Posted by tinsair
For any where it's not immediately possible to tell, I haven't confirmed them until I've seen a box. (For example, I'm fairly sure that The Majors: Pro Baseball had a European release, but still haven't seen a box and the cart is ambiguous. Unconfirmed until then!)