WHAT DOES 420 REALLY MEAN?? I've done a lot of searching around about the origin of the term "420". This Wikipedia article explains the myth the best.
The earliest use of the term began among a group of teenagers in San Rafael, California in 1971, calling themselves the Waldos, because "their chosen hang-out spot was a wall outside the school". The group first used the term in connection to a fall 1971 plan to search for an abandoned cannabis crop that they had learned about. The Waldos designated the Louis Pasteur statue on the grounds of San Rafael High School as their meeting place, and 4:20 p.m. as their meeting time. The Waldos referred to this plan with the phrase "4:20 Louis". Multiple failed attempts to find the crop eventually shortened their phrase to simply "4:20", which ultimately evolved into a codeword that the teens used to mean pot-smoking in general.
Reporter Ryan Grim, in The Huffington Post article "420 History: The Story Behind April 20 Becoming 'Weed Day'" documents the the "true" story behind the association at length. Grim quotes Steve, one of the original purveyors of the term:
"We'd meet at 4:20 and get in my old '66 Chevy Impala and, of course, we'd smoke instantly and smoke all the way out to Pt. Reyes and smoke the entire time we were out there. We did it week after week. We never actually found the patch."
But, Grim notes, they did find a useful codeword for their pastime. According to Steve:
"I could say to one of my friends, I'd go, 420, and it was telepathic. He would know if I was saying, 'Hey, do you wanna go smoke some?' Or, 'Do you have any?' Or, 'Are you stoned right now?' It was kind of telepathic just from the way you said it. Our teachers didn't know what we were talking about. Our parents didn't know what we were talking about."
The group had associations with the band the Grateful Dead, and it's been assumed that the band began using the term, spreading it among their followers. Later it was picked up by marijuana magazine High Times, and it wasn't long before it went viral.
So there you have it...420 ISN'T a police code for possession of marijuana.