It isn’t every day that you see a historical marker that commemorates local prostitutes. There’s one in Nevada City, though. It’s a small, hidden tribute to the city’s past as a wild gold rush town.

The plaque honoring the “ladies of the evening” is set just out of sight along a fence lining a hotel parking lot. It’s one of the many obscure, overlooked markers erected throughout the American west by the Ancient and Honorable Order of E Clampus Vitus (ECV).

The ECV, a fraternity dedicated to preserving the heritage western frontier, installs such plaques within places typically missed by more traditional historical societies. Though its members erect mementos honoring a wide variety of events and people (including a memorial to “Godzilla, King of the Monsters” at its former studio site and a plaque marking the Star of India as a California landmark), this plaque strikes an odd and questionable tone, given the group’s all-male membership.

Clampers—men who belong to this fraternity—celebrate each new plaque with a party. They celebrate quite often, drinks usually in hand, and are quite proud of their own confusion as to whether they’re a “historical drinking society” or a “drinking historical society.”

The organization first popped up in the 1800s, spreading throughout the gold mining towns before eventually dissolving after the Civil War. But it didn’t stay gone for long. In 1930, a new generation of Clampers revived the fraternity. Even now, it’s still going strong, with members dedicated to spotlighting forgotten pieces of the Wild West’s past.