This is a vintage Mexican sterling silver butterfly brooch.

markings visible on the back, "MEXICO," "STERLING," and "925," are hallmarks that indicate the brooch is made of sterling silver and its country of origin. 925 Sterling Silver: This hallmark means the piece contains 92.5% pure silver and 7.5% other metals, typically copper, which is the standard for sterling silver. The "Sterling" mark is often used interchangeably with "925". MEXICO: This marking identifies the piece as being made in Mexico, a country known for its silver jewelry craftsmanship, particularly from cities like Taxco. Maker's Mark: The symbol that resembles a stylized "W" is a maker's mark or a hallmark used to identify the specific silversmith or workshop. There were several systems for Mexican silver hallmarks, including a letter-number system, but some pieces may have a unique workshop logo or a numbered eagle mark.