Reprints of the ominous Ace of Spades cards that were air dropped over the Ho Chi Minh Trail or otherwise left with VC bodies. Vietnamese wording advises the VC to mend their ways...or else. Black on buff. You may have your own uses for these...

Skull symbolism is the attachment of symbolic meaning to the skull, generally the human skull. The most common symbolic use of the skull is as a representation of death and mortality.
Humans can recognize the fragments of a cranium in the earth, even when other bones look like shards of stone. The human brain has a specific region for recognizing faces [1], and is so attuned to finding them that it can see faces in a few dots and lines or punctuation marks; the human eyes cannot avoid recognizing a human skull as having once been human.
Moreover, a human skull with its large eye sockets displays a degree of neoteny, which humans often find visually appealing—yet a skull is also obviously dead. As such, human skulls have a greater visual appeal than the other bones of the human skeleton, and can fascinate even as they repel.
When the skull is represented in military insignia, the death's-head (Totenkopf) deals with the fear of death, but when tattooed on the forearm its apotropaic power helps an outlaw biker cheat death [citation needed]. The skull and crossbones signify "Poison" when they appear on a glass bottle containing a white powder. But it is not the same emblem when it flies high above the poop deck as the Jolly Roger: there the pirate death's-head epitomizes the pirates' ruthlessness and despair, their challenge to the natural order of things and to the inevitability of Death itself.
When a skull is worn as a trophy on the belt of the Lombard king Alboin, it is a constant grim triumph over his old enemy, and he drinks from it. Thus a skull is a warning when it decorates the palisade of a city, or deteriorates on a pike at a Traitor's Gate. The Skull Tower, with the embedded skulls of Serbian rebels, was built in 1809 on the highway near Niš, Serbia, as a stark political warning from the Ottoman government. In this case the skulls are the statement.