Epoxy should be nice for protection against gravel strikes and the like as well as keeping the color in place. But even a good UV-stabilized epoxy is likely to experience a little yellowing over five years or so, depending on your location. Here in Georgia, the sun will blast the hell out of anything left exposed in the summer, in fairly little time. What do you think about a layer of epoxy followed by a layer of liquid and/or spray varnish to provide maximum physical and UV protection?

Or they could just make the badges better.