Hi Alysia thank you for your question. More details and a photo would help. Is the antique ring made from silver, gold, pinchbeck. Is it plate, rolled gold, etc.
There are many marks on metals with crescent moons and dots. For instance, the Turkey Purity Mark on .800 & .900 SILVER - ca 1923 - 1928 is a crescent moon with a dot in the center which could easily be described as a half circle with a dot in the center.
