Bottoms Up Shot Glass, Summit
These are usually sold with a coaster. They're found in a variety of colors, both iridized and not. Iridized examples with the coaster sell on eBay for $10 to $15, without the coaster a bit less.

This red example, with a coaster, sold in 2021 for $50. A green opal example with a coaster brought $35.

Updated 11/15/2021