A "375" stamp on a piece of gold jewelry indicates that the metal is 37.5 percent gold. This is equivalent to 9 karats in the traditional method of marking gold purity.
Traditionally gold is stamped with a karat purity value. A 24k stamp indicates that the metal is 100 percent gold. Any karat amount less than 24 is divided by 24 to determine the percent of purity. Therefore 12-karat gold is 50 percent pure, and 10-karat gold is 41.7 percent pure. In gold pieces that are less than 10 karats, a number indicating the actual purity percent is often used instead of a karat amount, as in the case of the "375" stamp.