David Lieberman: That skull? That’s a memento mori. It’s Latin for, “Remember, you will die.” In Rome, victorious generals would return from war, and so they didn’t get blinded by glory, they’d have a slave who would say, “Remember, you’re only human. You are gonna die.”

Frank Castle: Well, that sounds good to me.

David Lieberman: Well, it’s meant as an admonition to value your life, to live it well.

From The Punisher – Season 1 Episode 11: ‘Danger Close’ (1×11)