Related from my own defunct blog: Skulls in military symbolism are actually not particularly odd, as indicators of toughness and ferocity (and in Navy a nod to the Jolly Roger, which was partly an identifier of the pirate vessel, but also a call to surrender with the promise of quarter...)

Discussing the M&W Are We The Baddies skit and the preponderance of skulls in Waffen SS kitch.