The Truth about why April 20th is "Weed Day." There are many myths about this day across the world. Depending on who you ask there are as many varieties of answers as strains of medical bud in California. It has something to do with Hitler’s birthday? It’s the number of active chemicals in marijuana? It’s teatime in Holland? It’s those numbers in that Bob Dylan song multiplied?

The true origin of the world-renowned term 420, celebrated by ever-loving pot smokers every April 20th, has long been unknown.

Some say 420 started with the Dead.

As luck would have it one source found all of the information from a Grateful Dead concert.

The week of Christmas 1990 there was a Grateful Dead Concert where a Deadhead handed out flyers stating, "We are going to meet at 4:20 on 4/20 for 420-ing..." and then further explained, "420 started somewhere in San Rafael, California in the late '70s. It started as the police code for Marijuana Smoking in Progress. After local heads heard of the police call, they started using the expression 420 when referring to the herb - Let's Go 420, dude!"

So there is your answer world, it came from the '70s police code