20 Dollars - Roy I Princess Joan I

Sealand — the former Royal Navy anti-aircraft platform HM Fort Roughs, seized by Paddy Roy Bates in 1967 and self-declared a sovereign principality — issued this coin the same year it survived an armed takeover attempt by former associates attempting to install a rival government. The "nation" had no central bank, no mint of its own, and no circulating economy; these pieces were struck by a private contractor and exist purely as novelty issues for the collector market.

X#2 in the Krause catalog places it squarely in the "Unusual World Coins" classification — a polite designation for issues whose claim to national authority is legally unrecognized by every UN member state.