It is a Model 1907 collar and hat device. They were used on hats and shirt and coat collars by all ranks. In October 1917 they were replaced by the disc shaped device on enlisted men’s collars, but retained for hats and caps. It remained standard for officers shirt and coat collars. The reason they were adopted in 1907 was to update the image of the rifles from the single shot models depicted earlier to the new bolt action rifle.