DAVID GREENE, HOST:
Good morning. I'm David Greene. If you're driving through Idaho and keeping track of progress, you might spot something weird - mile marker 419.9. Idaho officials put up those green signs because their 420 mile posts kept getting stolen. We presume by pot enthusiasts. Never been clear why 420 is linked to marijuana, though the BBC told the story of some high school students in California in the '70s who met at 4:20 to look for pot. Their friends were Grateful Dead fans and the story 420 grew among deadheads. It's MORNING EDITION. Transcript provided by NPR, Copyright NPR.