50 Cents Christmas

Redonda is an uninhabited volcanic rock in the Caribbean, roughly one square kilometer, whose "kingdom" is a literary fiction originating with M.P. Shiel in the late nineteenth century and perpetuated by successive self-appointed monarchs drawn largely from the British science fiction and fantasy writing community. It has no government, no population, and no monetary system. Coins issued in its name are souvenir pieces with no circulation history by definition.

The X# prefix in the reference confirms this: World Coin catalogers assign X-numbers specifically to non-circulating fantasy and local issues outside recognized sovereign authority.