Most gold, silver or platinum jewelry is stamped or hallmarked somewhere on the piece with letters or numbers that indicate the jewelry's purity. Gold will generally be hallmarked either 10k or 417, 14k or 585, 18k or 750, 21k or 875, 22k or 917, or finally 24k or 999. Silver or gold plated silver will generally be marked 925. Platinum will usually be hallmarked PT, PT900 or PT950. Items stamped 1/20GF are gold filled, and don’t have any resale value. A hallmark is usually a pretty good indicator of your jewelry's purity.