What does Shakespeare mean by memento mori?

In Act III, Scene 3 of King Henry IV, Part 1, Falstaff says, "I make as good use of it as many a man doth of a Death's-head or a memento mori . . ."

Modern readers may be familiar with the term Death's-head (a human skull used as an emblem of death, or a ring stamped with the picture of a skull), but not with the allusion to fifteenth-century funerary practices contained in the term memento mori.

Back then, affluent persons were represented in life-like sculpture — lying, sitting, kneeling, perhaps even on horseback — on the tops of their tombs. Sometimes, however, another sculpture was placed below the first: a representation of the deceased person's naked, decaying body. This was called a memento mori tomb, and it reflected the medieval obsession with the horror and corruption of death.