April 20 is here, and marijuana users might be celebrating in the usual fashion.

Since April is the fourth month, April 20 is commonly called "four-twenty." The number 420 also is part of the drug sub-culture code for smoking dope.

So much so that police departments issue warnings on April 20 to parents to make sure they know who their kids are hanging out with, when they get together and what they are up to.

"Many high school students are aware of 420 and we know some are making plans," said Middleton Police Lt. Noel Kakuske in a news release.

Why 420? The legend of 420 started in 1971 at San Rafael High School in California, according to rumor debunking website Snopes.com.

It was slang used by about a dozen pot smokers at the school for the time of day (4:20 p.m.) when they would get together to light up after school.

The number has nothing to do with police radio codes, state ordinance numbers, the day Jimi, Janis or Jim died (neither Hendrix, Joplin or Morrison died on April 20), or the best time to plant pot.

Kakuske said it might be a good day for parents to talk to their kids about drug use.

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"Parents just might be surprised by what they hear," he said. "As the parent who suggested this message reminds us, peer pressure is a powerful thing. Every year some nice kids from good families are drawn into the vortex of drug abuse."