Bang Bang was a brand of "heater" (gun) on Sigma Iotia II. They advertised on a radio program in which songs were played based on listeners' requests. 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")