Sorry Gianluca, it is a bit convoluted. They are dressed like pirates of the 18th century. Pirates steal treasure. One of the silver coins types that were around at the time was the Spanish silver dollar or "piece of eight" a coin worth 8 reals. Stay with me.. pirates are apochraphally known to have talking parrots, and one of the regular comedic interpretations of this trend has the parrot screeching pieces of eight, pieces of eight.
It's a British thing!