Free Unlimited Access promotion, the hat is a black tricorne Unlimited access members only were offered a special Black Buccaneer Hat. This hat was obtainable through the redeem code of BLACKHAT. The hat isn't really black though, it's more of a purple color. It it has a feather that sticks out of the back and a Skull and Crossbones on the front. The resale value is only 27 gold pieces.
Note: The code for this hat is no longer reedemable.