This is a coffee mug labeled "GROG" with a cartoon caveman face on other side. Grog was a character from Johnny Hart's BC comics (1958-2007) and this was a promotional item from Marathon Oil produced in the 70s. This is also a Fire-King piece. Fire-King is an Anchor Hocking brand of glassware similar to Pyrex. It was formerly made of low expansion borosilicate glass and ideal for oven use.