A pirate code, pirate articles or articles of agreement were a code of conduct for governing pirates. A group of sailors, on turning pirate, would draw up their own code or articles, which provided rules for discipline, division of stolen goods, and compensation for injured pirates. […]
Each crew member was asked to sign or make his mark on the articles, then swear an oath of allegiance or honour. The oath was sometimes taken on a Bible, but John Phillips’ men, lacking a Bible, swore on an axe. Legend suggests that other pirates swore on crossed pistols, swords, or on a human skull, or astride a cannon. This act formally inducted the signer into the pirate crew, generally entitling him to vote for officers and on other “affairs of moment”, to bear arms, and to his share of the plunder. The articles having been signed, they were then posted in a prominent place, often the door to the captain’s cabin.
Source: Pirate code – Wikipedia