1. The official currency of pirates. Almost always made of pure gold, but occasionally of silver as well. All have some form of the Jolly Roger struck on one side. The majority of pirate booty is gold doubloons.
2. In the United States, Sacajawea or Presidential dollar coins, especially new, shiny ones.
Pirate 1: Y'arr, what be yer share of the booty, matey?
Pirate 2: Eighty-five gold doubloons! ARRRGH!
Pirate 1: We'd best be gettin' to the tavern, then, there's a lot of wenching and drinking to do!
Pirate 2: Y'ARRRRRR!
Bob: I had to use a 20 in the ticket machine on the subway. Fuckin' thing gave me 18 doubloons for change.