Memento mori, Latin for: "remember you are only mortal". A motif used as decoration on various articles in the form of a reminder of mortality, e.g. as a coffin, a death's-head or a skeleton. Such pieces were not in remembrance of a departed person, but were an abstract warning of death, especially in the 16th and 17th centuries.
They include finger rings, brooches, enseignes, pendants, watch cases, pomanders, etc. The articles were usually mad eof gold with black enamelled motifs or set with gemstones.
From: An Illustrated Dictionary of Jewelry, autor: Harold Newman, publishers: Thames and Hudson