"Tart Cards": How The World's Oldest Profession Advertises

Long before Craigslist's Erotic Services section gave sex workers an easy way to advertise online (and then, ahem, took it away), the sex workers of London were advertising their wares through a creative medium known as tart cards.

Often found on the walls of London's iconic red phone booths, these advertising cards have been around since the 1980's—and have evolved over time, as changes in printing technology have allowed them to become more sophisticated and complex. "Tart Cards" has collected more than 350 of these works of art, providing some background on how they came about, how they've evolved, and what, exactly, "a-levels" refers to. Curious? Take a sneak peek inside in the gallery below.