This simple looking keychain is supposedly from the E3 of 1994, given out at the Sega booth to advertise for Sonic & Knuckles. You can see the copyright there on the bottom (looks legit) however the style of the keychain is unfortunate.
It may be the real deal, but this printed card in acrylic case type is EXTREMELY easy to bootleg. Beware of keychains in this style, even official ones can be flawlessly cloned due to their simple design.