Me. Rev. Stat. tit. 23, § 1908-A

A municipality may erect and maintain at a publicly owned bus stop outdoor advertising signs visible to the traveling public from a public way. For purposes of this section, "bus stop" means a place where a public transport bus stops for the purpose of allowing passengers to board or leave the bus. The municipality is responsible for the administration of outdoor advertising signs under this section. Any revenue collected under this section by a municipality must be used for transportation purposes, including, but not limited to, maintenance of a publicly owned bus stop.