1817 - 1820 Saint Martin 18 Stuivers, PCGS VF20, One Fifth Of An 8 Reales

That's really cool!

Specifically, it was made for half of that island.

Saint Martin is famous for several things - in this internet age, it's perhaps most famous for it's beachside Princess Juliana International Airport, with landing airliners flying so low over the beach they look CGI but aren't - but from the point of view of this coin, the island's claim to fame is that back in 1648 it was amicably split in half between the French and the Dutch, and remains thusly divided to this day; the French half is still part of France, and the Dutch half is now the mostly-independent country of Sint Maarten.

The name on the coin is given with the "French/English" spelling, but the denomination "18 stuivers" is definitely Dutch in inspiration. During the Napoleonic wars, both halves of St Martin were annexed by Britain, but by 1817, the British had already handed back both halves to their previous owners. All the countermarked coins in the name of Saint Martin appear to have been produced for the French half of the island.

I don't see the 18 stuivers stamp. Is it that thing that looks like a sunburst?

Especially interesting because as Sap said, if the coin was intended to circulate on the French half of the island, why 18 stuivers? (instead of, say, 2 francs which would have been the French equivalent).
Also interesting because the stuiver ceased to exist in the Dutch currency system after 1817 when the guilder was decimalized.