Bang Bang was a brand of "heater" (gun) on Sigma Iotia II. They advertised on the radio program "Request Time". Their slogan was "the sweetest little automatic in the world".
Spock caught a snippet of the radio program when he and Dr. McCoy were attempting to contact the USS Enterprise and, with a degree of distaste, gave his usual reaction: "Fascinating." (TOS: "A Piece of the Action")
The radio announcer promoting "Bang Bang" was the voice of James Doohan. His Scottish accent creeps into the dialogue in the last word "world", just before Spock shuts off the broadcast. (The Star Trek Compendium)