What does 420 mean? Where did 420 come from? Before we get into the history, let's debunk some of the myths surrounding 420: Police use the radio code "420" to report a marijuana smoking in progress This is the most popular myth surrounding 420 but it's just that: A myth. While there are some standards, police codes differ by state, county and local department and not all of them use code no. 420. In Las Vegas, police officers use 420 to call in a homicide. In San Francisco, it's a juvenile disturbance. Many New Jersey police departments, including the State Police, don't even use code no. 420. While there may be a few police dispatchers in the United States who get a laugh out of assigning marijuana offenses to code no. 420, they're the exception to the rule.