What does Fo mean on a gold ring?

The marking "Fo" on a gold ring typically indicates that it is made of gold that is alloyed with other metals, and it may refer to a specific standard or manufacturer. However, it is not a commonly recognized hallmark like karat markings (e.g., 10K, 14K, 18K) and may require further research or context to determine its exact meaning. Always consider consulting a jeweler for accurate identification and appraisal.