Origins. In 1971, five high school students in San Rafael, California, used the term 4:20 in connection with a plan to search for an abandoned cannabis crop, based on a treasure map made by the grower. The Waldos referred to this plan with the phrase 4:20 Louis.

Why is there no room 420 in hotels?

The reason is that 420 related items have become stoner trophies. Road signs are one target: road markers bearing the number 420 in Colorado have had to be replaced with 419.99, for instance. Hotel rooms have become another, forcing some hotels to phase out the room number altogether.