In Nov. 2012, a statewide ballot initiative approved adults age 21 and older to have up to one ounce of usable marijuana.
Even before that, Metro would occasionally find marijuana left on buses - typically small amounts in backpacks or film containers, sometimes with a pipe. That was turned over to police, and amounts over 1 ounce still will be, Metro spokesman Jeff Switzer said Friday.
"People can't just come to lost and found and say, 'I lost some pot,'" he said. "They will need to provide a lot more information before we reconnect them with that lost and found item."
Metro has roughly 200 bus routes, and riders trying to reclaim their missing weed will have to say specifically the route and time when they lost it. No one has tried to pick up pot from Metro's lost and found yet.
In an average year, Metro has about 40,000 lost and found items, with the most common being black umbrellas. But they also come across cell phones and laptops often, and sometimes even the more bizarre: dentures, personal items, and prosthetic limbs.
The biggest month for bikes left on the front of Metro buses is in August - the same month hundreds of thousands of people pack Myrtle Edwards Park for Hempfest.
The change in the lost and found policy came about in March for lost and found employees who came across pot in backpacks or other bags. Drivers were alerted to the change in a policy bulletin this week, Switzer said.
Earlier this year, Seattle police gave back the small amount of marijuana confiscated from several suspected marijuana dealers during a sweep of dealers in the University District last week.
Medical Marijuana has been legal in Washington since 1998, and another voter initiative in 2003 made marijuana arrests and prosecution the lowest priority of the Seattle Police Department when the drug was intended for adult personal use.