One of these buses was assigned to a route that had a bus stop on Columbus Avenue. It bore on its right side an advertising sign for the Cetacean Institute. Admiral James T. Kirk and Captain Spock attempted to board this bus, but were kicked off because they didn't have exact change.
Another one of these buses was assigned to an express route between San Francisco and Sausalito. This bus bore an advertising sign on its front for the Marvel Comics character Quasar. Kirk and Spock, after getting exact change, rode this bus to the Cetacean Institute in Sausilito. (Star Trek IV: The Voyage Home)