Horseshoe
This 3 5/8-inch tumbler is named for the horseshoe molded into the bottom. There is also a version without the horseshoe, referred to as unshod. This one sold at Bob Smith's tumbler auction in 2019 for $5; an unshod example went for $2.50.

Bob elsewhere pointed out that he had discovered that at least seven companies made such a pattern.

Photo courtesy of Wroda Auctions

Updated 7/21/2019