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.