420: America's cannabis lovers light up on unofficial stoners' day

Countless Americans are sparking ablaze their joints, glass pipes, and spliffs in observance of the official holiday for cannabis, 20 April, more commonly known as 420.

The number’s origin is often contested. Many people believe that it is comes from a police code for “marijuana smoking in progress,” for example. The San Francisco Chronicle, however, links the term to an obscure group of students from the 1970s known as “The Waldos.”

The San Rafael, California, teens muttered the codeword, “420 Louis,” to each other in hallways of their schools. This meant planned to meet outside at 4:20 in the afternoon in front of a statue of famed scientist Louis Pasteur that stood on school grounds.. From that point, the group would embark on their journey to procure a bag of the plant.

But what once stood as the signal as a clandestine adventure amongst some teens to buy a bag of cannabis is now a celebrated number amongst pot-enthusiasts - many of whom observe the holiday publicly via social media.

Between Instagram and Twitter, 420-observers share the contents of their morning rituals and day-long recreation. The photos are similar - a plume of smoke, a green chunk of dried-up leaf inside of a glass pipe, the joints, and usually a lighter.

Celebrities also join in on the celebration. Some are known for their enthusiasm for cannabis - like rappers Snoop Dogg and Wiz Khalifa - and others may seem out of character - like Megadeth frontman Dave Mustaine.

Naturally, no Internet celebration would be complete without the memes.