The long bowmen of the medieval age used it for drawing their bows and called it their plucker. To annoy the opposing forces the would show it off that they still had it owing to the opposing forces would cut them off every chance they could.
Are you talking about 'flying the bird' or 'flipping off' or 'giving the finger'? If so this gesture dates all the way back to ancient Rome where it represented a phallus and anal intercourse and, as today, was an insult. Some countries like England, have adapted it to two fingers (middle and index) with hand held backwards for proper form.