Because the San Francisco Municipal Transportation Agency (SFMTA) has a rule against ads that "appear to promote the use of firearms," movie studios often have to create special gun-free editions of posters advertising their new releases. In the San Francisco versions of posters for the 2010 cop comedy The Other Guys, for instance, Columbia Pictures replaced guns held by stars Will Ferrell and Mark Wahlberg with badges and pepper spray canisters.
The SFMTA never realized there might be a constitutional problem with this firearm-phobic policy until Alan Gott-lieb of the Second Amendment Foundation, upon learning that Ferrell and Wahlberg had been disarmed, printed up a bunch of ads for the group's September gun rights conference in San Francisco. They featured a woman holding a shotgun while peering through a curtain in her home, under the headline "Can You Afford to Be Unarmed?" The posters went up unchanged at bus stops around the city, and the SFMTA announced that "we are currently reviewing our advertising policy in light of the recent Supreme Court decision, which may have altered the legal landscape regarding firearm advertising."
Oddly, the SFMTA was referring to McDonald v. Chicago, the 2010 decision in which the Supreme Court said the Second Amendment protects an individual right to arms that cities and states must respect. The transit agency should have been thinking of the First Amendment instead. Federal courts have long taken a dim view of content-based restrictions on speech in a "designated public forum" (such as a transit agency's advertising space), especially when they discriminate against a particular viewpoint, as a ban on ads that "appear to promote the use of firearms" does.