In the early 1970s Citizen produced their ‘Challenge Golf’ models – with a score counter complication  and high-beat (28,800 beats per hour) these are interesting and possibly unique watches. With round or ‘tv’ style dials they use the 7760 movement, part of the ‘Leopard’ family, in black coated cases with either gold or stainless steel bezels. See here for more info: https://sweep-hand.org/2011/06/07/this-weeks-featyured-watch-6-the-challenge-golf/

Although some of them have conventional case backs, many have a recess on the back, apparently designed for a medallion. But one of my examples, as with all the others I’d seen, have no medallion:

But recently an example sold on Yahoo Japan – with a medallion! But it’s not a conventional medallion – it’s an insert that can be personally engraved for example to mark a competition victory:

This is the only example of this watch with the medallion in place I’ve seen, but you only need to see it once to solve the mystery 🙂