There's nothing inherently funny about mile 420 on the highway. But ever since the code between high schoolers looking to get high after class became a universal symbol of marijuana culture, every instance of 420 has become a stoner punch line—including innocent mile markers. Not all states have long enough highways to necessitate a "Mile 420" sign, but those that do have a shared, recurring problem: People keep stealing them.

The Associated Press reports that Idaho has recently joined states like Washington and Colorado in efforts to replace "Mile 420" signs with "Mile 419.9," which are not nearly as popular with cannabis enthusiasts.

Adam Rush of the Idaho Transportation Department confirmed to the AP that this was an unusual move for them. "Having a sign removed from a highway is pretty rare," Rush noted. "In Idaho, people will shoot at them or write on them before stealing them completely. We spend more time mending signs than replacing them."

In Washington, one of the two 420 mileposts in the state was replaced in 2012, the same year it legalized recreational marijuana use. The sign that was not replaced has since gone missing.

"Obviously people steal these signs," Colorado Department of Transportation spokeswoman Amy Ford told the Denver Post last year after the state replaced its only "Mile 420" sign. "In the past, if a sign was stolen too much, we wouldn't replace it. This is sort of an innovative way for us to keep the sign there."

Innovative, but not unprecedented, as Jamie Fuller of New York Magazine notes. In Colorado, the practice of replacing potentially salacious signs with more innocent fractions actually started when Mile 69 had to be replaced with Mile 68.5.

[h/t New York Magazine]