This is the Moustache Guard. In 1876, a West Virginian named Virgil A. Gates filed a patent for his invention, with the purpose of 'holding the moustache out of the way of food or liquid while eating or drinking.' He also noted that the guard could be made of metal, rubber, or 'any other suitable material, of proper size to fit over the upper lip and moustache.' The guard was held in place over the moustache by two elastic cords fastened over the ears, as shown in the illustration.
Guinness conducted a study that found drinkers with mustaches, on average, lost 1.5 pints of beer (in their mustaches) annually.