That is a 1972 CB750 K2 one year only switch. And yes, it is to stop the turn buzzer.
K1s did not have that switch, so somebody borrowed it, or swapped the whole handlebars. K2 is the last year of single fuse wiring with lights off/low/hi on the right side of handlebars. You can use that switch on K0s as well, but nobody will.