It was a private signal that became a worldwide symbol. In 1971, five teenage boys at San Rafael High School created a code, 420, for the time to meet after school, get high and search for a plot of illegal marijuana planted by a member of the Coast Guard, whose map to the grow and permission to harvest it had found its way to them. The code was a way for the boys, who nicknamed themselves the Waldos after a wall where they sat cracking jokes between classes, to talk about cannabis without adults knowing what they were up to. They whispered, “420 Louis” to each other in the halls, and met at the statue of Louis Pasteur in front of the school. Their quest for the pot patch ended without success, but the code took on a life of its own and — thanks to the teens, their friends and even the Grateful Dead — spread around the globe in the decades after. Heads of the class: High school kids created 420 decades ago — now they tell the tale