The Black Flag is traditionally related to piracy

https://usc1.contabostorage.com/2a53d746ab14419ca1f7a73582a9e3d4:dashdfljksdf/ultimate-flags-revolutionary-war-flags.html

The Black Flag is traditionally linked to piracy and anarchy; it turned into utilized by buccaneers to signal no mercy toward their enemies, fitting a long-lasting image of riot opposed to authority.