A memento mori (latin: remember that you must die) is a object or pictorial symbol associated with death. Such symbols include skulls, bones, coffins, urns, angel of death, upside-down torches, graves and ravens, cypresses, weeping willows, tuberoses, parsley, and many more. A good number of these associations can be traced back to antiquity.
These emblems of mortality have long been used as items of adornment: Mary, Queen of Scots, owned a skull-shaped watch; Martin Luther had a gold ring with a death’s-head in enamel; even today skull motifs are used in al sorts of jewelry and bric-ŕ-brac. The idea that everything and everybody in this world were heading towards death produced and reflected both a complacency in the face of death and anxiety about the oblivion of death.
The mourning rings would often have a small receptacle in the center for a locket of hair from the deceased. Hair has been collected from the dead since the beginning of times. Hair signified the vanity of this world; it reminded people of death; but they nevertheless embellished their hair with golden dust to forget about death. Some says that God decided to put hair on the human being's head as a flag of death. When we are overwhelmed by an illness, sorrow or trouble (the above things are the fangs of death), we instinctively grab our hair and tear it out as if reminding ourselves about death.
There was a custom reputed to be in use in Imperial Rome, of having victorious generals accompanied in their triumphal processions by a slave, who would constantly repeat the cant, 'Remember thou art mortal'.
The idea of the omnipotence and omnipresence of death was reflected in the exhaustive repertoire of images assigned to the mors. The argument for daily dying was a certain protection against being caught unprepared: "Death is an old enemy of human life; if you don't want to be taken by surprise, beware and watch him from afar, as from a guardtower."