Please study the meaning of the "Skull and Bones" and you will find the following:
1. The Templar Knights once betrayed by the Pope and the French king, the surviving knights ran to the sea and became pirates.
2. The adopted the skull and bones, representing their patron, John the Baptist (who was beheaded by the Romans), as their symbol.
There is more to the story. But, I don't have the time right now to keep on typing.