Romani's Mask
From Zelda Legends Wiki
Romani's Mask is a mask in The Legend of Zelda: Majora's Mask. It has the shape of a cow's head and Link wears it over his face, so it does not cover his face. It is used as the membership required to enter to the Milk Bar. You get it from Cremia on The Second Day after helping her deliver the milt safely to the Milk Bar.