The history of the symbol dates back to the 1700s, when the entrances to Spanish cemeteries were marked with actual human skulls and bones. This 'campo santo' practice led to the symbol being associated with death. The sign was engraved on tombstones across Europe. Many crucifixes were designed to feature the symbol beneath the corpus or depiction of Jesus' body. Most of the Christian associations with the symbol come from the mention of the place of Christ's crucifixion as 'Golgotha' or the place of a skull, in the New Testament of the Holy Bible (Mark 15:22).
The 1732 Nuestra Señora del Pilar church, that overlooked the Recoleta Cemetery, Buenos Aires, Argentina, was designed to depict the symbol. By the 1800s, the sign was used to label containers of poisonous substances, alongside the 'XXX' symbol. In the nineteenth century, the presence of the symbol on poison bottles became ubiquitous. It was also used by military forces on 'Jolly Roger' submarine flags, reconnaissance battalion emblems and fighter unit aircraft tails. Today the symbol is one of the most recognizable squadron markings.