This is likely some kind of event-sponsoring / event give-away prize pin.
It has both the Kellogg's (cereal) & Sega logo on one side. It's mostly brass-tone metal, with 4 colors of enamel for the Sonic art. This art doesn't fare as well, as it relies on the background color (metal) to define the lines for the art, so you can see how easily his shoe bottoms (Feet look too thin), finger tips on folded hand (finger number unclear) & eye edge just get lost because the border is also the background color. However, it is still clearly Sonic, and the die-cutting for the edge around his spikes gives the whole design some nice interest. (Especially for something early like this, that's also some kind of sponsorship deal) What was this pin for? How could you get one?