4:20 originated in San Rafael. What happened was, a group of guys who went to San Rafael High School in 1971 would smoke weed at the Louis Pasteur statue at San Rafael High School, and every time they did this they would do it at 4:20 PM. They would later come up with the term "Louis 4:20" to use when on the phone around their parents or near authoritative figures. It would later become a world wide phenomenon (how it did is beyond me) were stoners would smoke up on April 20 (4/20) at 4:20 AM/PM (depends on how early you wake up). Lastly, 4:20 is not a police code for pot or any other drug.
"Dude, let's get blazed at 4:20 AM and PM man!"
"Alright man! Wait. How the fuck are we gonna make up that early?"
"Oh shit. Fuck. Uhhhhhhhhhhhh. Shit. Oh! I got it! I'll set an alarm!"
"Dude, that's some fuckin' Einstein shit right there bro!"