Interesting look at the origins and purpose of the skull and crossbones. An excerpt from near the beginning of the report:
Captain Cranby’s report is one of the first recorded sightings of a pirate’s flag emblazoned with a human skull and pair of diagonally crossed bones. During the early 1700s, those symbols were adopted (usually without the hourglass) by pirates worldwide in an astonishingly successful exercise in collective branding design.
The key to its success was clarity of meaning, which is an essential element in every effective branding project, and any other form of communication design. Just as Nike’s “swoosh” logo makes us think of speed and the horse-drawn carriage in Hermès’s identity screams posh, the sight of a skull and crossbones on a ship’s flag signaled one thing to 18th-century sailors like those on the Poole or the merchant vessels they were protecting: terror.