The origins of the ubiquitous skull and crossed bones symbol are unclear. The symbol itself is quite old, and appears as a funerary symbol in christian catacombs. In the middle ages, it was a common tombstone decoration, and appeared in many “memento mori,” illustrative reminders of mortality. In more recent times, the skull and crossbones signifies poison.
Another common appearance of the symbol is on the “Jolly Roger,” or pirate’s flag, the so-called “Jolly Roger,” is believed to have been named after the jolie rouge, the name French Templars gave the red flag flown by Templar warrior ships, and later co-opted by pirates. The significance of the symbol to the Templars is not known, but bodies in Templar graves have been found with the legs removed and crossed.
The skull and Bones and Freemasonry
The skull and crossbones is also an important emblem in Masonry, where it symbolizes the transience of the material world, and is used in initiation rituals as a symbol of rebirth. It may also symbolize the sephirah daath on the kabbalistic Tree of Life, the gateway to the higher realms of understanding only achievable through spiritual death and rebirth.
In hermetic kabbalah, the skull and bones are related to the Chi-Rho, symbolizing time,death, and rebirth.