Memento mori jewelry was designed as a reminder of the transience of life and the importance of faith, and was often used as mourning or wedding (!) jewelry. It was extremely popular during the Victorian era, so most of what you can find today is from that period, and I hadn’t realized how old the tradition was.
From the V&A exhibit:
• Ring, 1550-1600, gold, chased and enameled, made in England, and inscribed “BE HOLD THE ENDE” and “RATHER DEATH THAN FALS FAYTH”
• The Torre Abbey Jewel, 1540-1550, gold with enamel, made in England, and inscribed “THRONGH.THE.RESVRRECTION.OF.CHRISTE.WE.BE.ALL.SANCTIFIED”