What is the value of a herringbone necklace with 925 GM stamped on it?

A herringbone necklace stamped with "925 GM" indicates that it is made of sterling silver, which is 92.5% pure silver, with "GM" possibly referring to a manufacturer's mark. The value of such a necklace depends on its weight, craftsmanship, brand, and current market prices for silver. Generally, sterling silver jewelry can range from $20 to several hundred dollars based on these factors. For an accurate valuation, consider consulting a jeweler or appraiser.