Vintage Sterling Silver "Dec 25" Enamel Christmas Bracelet/Necklace Charm

This listing is for a vintage Sterling Silver charm with red enamel. It's a scalloped disc shape about the size of a 10-cent coin and rewards "Dec 25." This charm is in excellent vintage condition. It is marked Sterling ("STER") on the back and doors have some kind of brand/maker's mark, but I've been unable to decipher it.