the weed on the bus goes round and round, all around town

A couple folks complained about an Oly Hempfest ad on the side of an Intercity Transit bus. The agency isn't backing down, though; the ad clearly represents political speech, even though it includes--horrors!--a photo of a cannabis leaf. What's out of bounds:

Intercity Transit forbids advertising on its buses that is obscene, defamatory, racist, sexist or "that is directed at producing imminent lawless action and is likely to produce such action." The agency does not endorse any issue or product advertised on its buses, the exception being self-promotion, according to its policies. All political and issue advertisements identify who sponsored them.

If looking at a pot leaf promotes "imminent lawless action," then what will we make of all those anti-drug ads sporting drug paraphernalia? Consider the top half of a recent print ad, which, at first (and potentially only) glance, has a message bound to boomerang:

Today's weed: twice as efficient!