Thieves think it's funny to steal signs marking a southeast Missouri highway whose number is often associated with drug use. Highway officials don't see the humor.

Signs for Scott County Road 420 disappear routinely despite some extraordinary measures to thwart thieves. The number 420 is often associated with marijuana — it is generally believed to be the time of day that, in 1971, a group of California high school students met to smoke the drug. The number has since become an international slang term.

Highway administrator Norman Brant has tried surveillance cameras and motion-sensitive lighting. He even had workers slather cow manure on the poles.

"That kind of backfired on us because the manure dried up," Brant said.

Nothing has worked. Now, three new signs are welded to 8-inch steel pipes. Workers on Wednesday pounded the sign posts into the ground by a backhoe shovel.

The thefts are more than a nuisance, Brant said. He recalled how a nighttime ambulance call nearly went unanswered because paramedics couldn't find the road without the sign.

"The people in the house could see the ambulance lights in the distance, going back and forth on Route CC," he said. "Finally the driver guessed at a gravel road and he was right."

Other counties face similar problems with their roads numbered 420. Only two signs mark Cape Girardeau's County Road 420 as it rises and dips for three miles from Route B, south of Route KK, all the way to Bollinger County.

Cape Girardeau County highway administrator Scott Bechtold said he "naively thought thieves were after the aluminum signs for recycling." So he ordered replacement signs made of wood. Those disappeared, too.

He said new signs cost about $30 each.

Changing a road name to something less attractive to drug users and pranksters would be complicated, Brant said, noting that all deeds and maps would have to be changed, along with Global Positioning System information. All the property owners along the road would have to be contacted.

Cape Girardeau County Prosecuting Attorney Morley Swingle said stealing a road is a misdemeanor, unless the value of the item taken is more than $500, at which point the crime becomes a felony.