A hallmark is not decoration. It is a small, standardized statement: this piece is 925 sterling silver, or 750 gold, or 585 gold, made by this workshop, assayed in this city, in this year. The numbers have meanings that do not vary: 925 means 92.5 percent silver, 750 means 18 karat gold, 585 means 14 karat. Counterfeiters copy the numbers, but they copy them onto pieces that fail the checks the numbers imply, and that gap is where monitoring teams work.
The first check is whether the stamp agrees with the piece. A hallmark that says 925 on a piece that is magnetic is lying, because silver is not magnetic. A hallmark that says 750 on a chain that weighs half what a gold chain of that length should weigh is lying, because gold is dense and the weight is the metal. A stamp in the wrong font, crooked, or shallow where the genuine house stamps deep and straight, is the third tell. None of these checks proves a piece alone. Together they are a stack, and a genuine piece passes the whole stack.
Counterfeit jewelry concentrates where the margin is widest and the buyer is least equipped to check: gold chains and bracelets sold below the metal price, gemstone pieces where the stone is glass or synthetic and the setting is plated base metal, and branded pieces where the brand, not the metal, is what the buyer is paying for. A gold chain at half the price of the gold in it is not a bargain. It is a piece with no gold in it, and the price is the giveaway before any test is run.
Marketplace listings are the main channel, because a listing can show a genuine hallmark photo taken from a real piece and ship a different one. Monitoring teams treat the listing photo as a claim, not as evidence, and they check the seller instead: how long the storefront has existed, whether it sells one brand or fifty unrelated ones, whether the reviews cluster in a single week. A storefront that appeared last month selling fifty brands of jewelry is not a jeweler. It is a storefront.
Ask for a photo of the hallmark, sharp enough to read, and a photo of the clasp and the back of the setting. Compare the hallmark format against the assay office's published format: the shape of the punch, the letter for the year, the sponsor's mark. Weigh the piece if you can, or ask the seller for the weight and compare it against a genuine piece of the same design. Run a magnet over it: gold and silver are not magnetic, and a piece that sticks is plated steel.
Then check the price against the metal. The price of gold is public, and the weight of the piece is knowable, so a piece priced below the value of the metal it claims to contain cannot be what it claims. That arithmetic is the fastest check in the whole stack, and it is the one buyers skip most, because the bargain is the point. Monitoring teams do not skip it.
Report the listing to the marketplace with the specific discrepancy: the hallmark format does not match the assay office record, the weight is inconsistent with the claimed metal, the seller's storefront is days old. A report that names the check is acted on faster than a report that says fake. Keep the evidence packet: the listing screenshots, the hallmark photo, the weight, the seller history. That packet is what turns a takedown into a pattern, and patterns are what get storefronts removed instead of relisted.
If this topic is useful, these earlier guides go deeper on connected questions: Counterfeit Supplements: The Category Where Fakes Can Hurt Fastest, What Test Buys Actually Say About the Counterfeit Rate, and Counterfeit Toys: Why Monitoring Teams Check for Lead Before Logos.
Check the hallmark format against the assay office record, compare the weight against a genuine piece of the same design, and run the price against the public metal price. A piece priced below the value of the metal it claims to contain cannot be what it claims.
They are fineness marks: 925 means 92.5 percent silver, 750 means 18 karat gold, and 585 means 14 karat gold. A hallmark should also name the maker and, in many systems, the assay office and year.
Gold and silver are not magnetic, so a piece that sticks to a magnet is plated base metal, not solid gold or silver. It is one check in a stack, not a verdict alone, but it is a fast one.
The specific discrepancy, not just the word fake: the hallmark format does not match the assay record, the weight is inconsistent with the claimed metal, or the seller storefront is days old. Include listing screenshots, the hallmark photo, and the seller history.