Graham Gilmor, brother of famous Confederate cavalry officer Harry Gilmor, modified his .44 caliber Remington revolver with a loop at the base of the grip for a lanyard, and more uniquely, with a custom rear sight.
The large round sight would make it much easier to focus on a target while riding a horse. The crosshairs appear to be made of a natural fiber—perhaps silk or even horsehair?
A gunsmith had to mill a groove into the flat top of the Remington’s frame to install the sight. The small hole in the top of the sight let in a bit of light.