People in the Renaissance had their very own wacky ideas about the meaning of moles. Quack Richard Sanders invented a faddish "system" by which he claimed people could use facial moles to find out where people had corresponding birthmarks.
At the time, birthmarks were believed to give deep insights into personality. So if you could find out where someone's moles were, you'd know where their birthmarks were, too, and then could use them to discern whether someone would make a good husband, business partner, etc.
The 18th Century
The Victorian Era
The 1950s were a time of buttoned-up sexuality, and Marilyn Monroe, the era's greatest sex symbol, quickly became known for the off-center mole on the left side of her mouth. A century before, moles near a person's mouth denoted high levels of sensuality, and the association was still clearly hanging around in the 20th century.
Now, however, instead of being a negative trait, moles like Marilyn's became sexy, inciting a generation of young women to draw them on for a little extra sex appeal.