Hanging on someone's bedroom wall - maybe on a lot of bedroom walls - is a sign from southern Minnesota that says "420th Avenue" or "420th Street." That might not mean anything to mom or dad, but to a stoner, it's far out.

Officials in three counties noticed a problem a few years ago. The signs marking rural roads as "420th Avenue," "420th Street" and even "420th Lane" were disappearing.

It turns out that the number 420 carries a special significance in the marijuana subculture. The reasons are foggy, as one might expect, and urban legends abound.

With sign replacement costs averaging $80 to $100, officials decided it was high time to take action - by changing the street names.

Waseca County recently decided to change the names along the 11 miles of 420th Avenue to 42Xth Avenue. Le Sueur County officials renumbered their 420th Street and 420th Lane to 421 about a year ago.

"I drove most of the road yesterday," said Brad Milbrath, chief deputy for the Waseca County sheriff's office, "and all the signs were up."

Steven Hager, editor of the marijuana magazine High Times, contends the use of "420" as a code of marijuana apparently originated in San Rafael, Calif., in the 1970s.

In an interview posted on the High Times Web site, he debunked a popular theory that 420 was the San Rafael police department's radio code for marijuana. He gave greater credence to a claim by a group of people from San Rafael High School who met every day after school at 4:20 p.m. and used the number as a secret code so they could talk about marijuana in front of their parents and teachers.