If you were a kid in the 1970s, you may recall the Marvel medallions. There were a couple of them. Here's the Spider-Man one. It was a large coin, in a removable ring and chain. You could wear it or pop the medallion out and carry it in your pocket.
All Biglee has come across this rarely seen art for the Fantastic Four medallion by Marvel Art Director John Romita.
Related: Not to be outdone, nearly a decade later, DC Comics offered a series of Medallions in these 1988 in-house comic book ads upon the occasion of Superman's 50th birthday: