NEW YORK, April 20 (UPI) -- There is increasing acceptance of marijuana in the United States, say some advocates, who Monday marked an unofficial day of celebration.

The April 20 ritual dates to the 1970s when a group of Northern California teenagers smoked marijuana daily at 4:20 p.m., The New York Times reported Monday.


As the ritual spread in popularity, marijuana fans began using "420" as the code for smoking pot and designated April 20 as a day of celebration.

Today, 420 is openly celebrated at many colleges and in many cities, with some advocates of legal marijuana saying they sense greater acceptance of the drug, either as medicine or entertainment.

"There's a sense that the notion of legalizing marijuana is starting to cross the fringes into mainstream debate," said Ethan Nadelmann, executive director of the Drug Policy Alliance in Washington.

Police in many cities, however, said they would be on heightened alert Monday for people reveling in 420 celebrations. In Kansas City, for example, police planned to saturate the streets looking for drivers under the influence of marijuana, The Kansas City Star reported.