(CNN) - There is something in the air today. Maybe you've noticed.
April 20, or 4/20, is known as "Weed Day" in some circles because the date corresponds with a numerical code for marijuana.
Yes, it seems arbitrary. So how did the number 420 come to represent smoking pot?
First, let's get the myths and rumors out of the way:
The legend of the California penal code
Some claim 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. So, not quite.
But the rumor sounds a lot like ...
The legend of the police radio code
Neither LAPD nor NYPD even have a code 420. San Francisco Police has one, but it's for a "juvenile disturbance."
So never mind that theory.
Then there's ...
The legend of the Dylan song
This one is a nod to Bob Dylan's song, "Rainy Day Women #12 & 35" and its lyric, "Everybody must get stoned."
Multiply 12 by 35 and you get 420.
Seems a bit of a stretch. And Dylan himself has never confirmed any link.
The story that appears to hold the most water is ...
The legend of the Waldos
According to Chris Conrad, curator of the Oaksterdam Cannabis Museum in Oakland, California, 420 started as a secret code among high schoolers in the early 1970s.
A group of friends at San Rafael High School in Marin County, California, who called themselves "the Waldos," would often meet at 4:20 p.m. to get high.
For them, it was an ideal time: They were out of school but their parents still weren't home, giving them a window of unsupervised freedom. They met at that time every day near a statue of Louis Pasteur, the scientist who pioneered pasteurization.
The 4:20 time became a code for them to use in front of their unsuspecting parents, and 420 gradually spread from there -- possibly via Grateful Dead followers -- across California and beyond. It's even the number of a California Senate bill that established the state's medial marijuana program.
What was shorthand for a group of friends can now be seen on T-shirts, in Tinder bios (420 friendly) and throughout pop culture.
And of course, on the calendar every April.