This is a vintage Reese's milk chocolate peanut butter cup advertising ceramic mug. It is 3" wide and 3 3/4" tall. It is marked on the side near the handle "Reese's is a trademark of Hershey Foods Corporation, Billco Int'l., licensee." The mug is in excellent condition. Reese's was purchased by Hershey in 1963, so this mug can't be any older than 1963. I think it is a 1970s-80s piece.
Reese's Milk Chocolate Peanut Butter Cups Mug Made in Japan