April 20th has become known as Weed Day in some circles because the date corresponds with a numerical code for marijuana.

There have been many rumors  and myths about how the  the number 420 come to represent smoking pot. Such as:

The number is drawn from the California criminal codes used to punish the use or distribution of marijuana.

But the state’s 420 code actually applies to obstructing entry on public land.

another  rumor….

It’s a police radio code for drugs.

Neither LAPD nor NYPD even have a code 420. San Francisco Police have one, but it’s for a “juvenile disturbance.”

The most credible story traces the date to Marin County, Calif. In 1971, five students at San Rafael High School would meet at 4:20 p.m. by the campus’ statue of chemist Louis Pasteur to partake. They chose that specific time because extracurricular activities had usually ended by then. This group—Steve Capper, Dave Reddix, Jeffrey Noel, Larry Schwartz, and Mark Gravich —became known as the “Waldos” because they met at a wall. They would say “420” to each other as code for marijuana.

Later, Reddix’s brother helped him get work with Grateful Dead bassist Phil Lesh as a roadie, so the band is said to have helped popularize the term. On Dec. 28, 1990, a group of Deadheads in Oakland handed out flyers that invited people to smoke “420” on April 20 at 4:20 p.m. One ended up with Steve Bloom, a former reporter for High Times magazine, an authority on cannabis culture. The magazine printed the flyer in 1991 and continued to reference the number. Soon, it became known worldwide as code for marijuana. In 1998, the outlet acknowledged that the “Waldos” were the “inventors” of 420.