“Participants will then engage in a token toking gesture of lighting up their blunts exactly four minutes and 20 seconds into Trump’s inaugural speech, the group’s founder said.”
The number 420 is not police radio code for anything, anywhere.
Checks of criminal codes suggest that the origin is neither Californian nor federal.
For instance, California Penal Code 420 defines as a misdemeanor the hindrance of use of public lands.
Source: https://modernmanchild.wordpress.com/2012/04/20/420-facts-vs-myths/
https://en.wikipedia.org/wiki/420_(cannabis_culture)