Today is April 20th. 420 is a text code to signify illegal drug use or more specifically the use of marijuana. From that April 20th has counterculture holiday.
But where did the term come from.
According to snopes.com it started to be used by a group of students at San Rafael High School in California as the time, 4:20 in the afternoon, that they would get together to smoke some weed. This was way back in the early 1970s. 1971.
Also on snopes it is said not to have any relationship to police codes for marijuana use in progress
The California Bill that legalized the use of medical marijuana is Senate Bill 420, but it was signed in 2004, long after the term was in use. Although I suppose some may have started using the bill number without realizing that the term was already being used by others.
April 20th is also the birthday of one of the most despised man in History. Adolf Hitler was born on April 20, 1889.