Short answer
A counterfeit Cartier Must de Cartier is a watch that carries the Cartier name on the case, dial or caseback without Cartier authorization. The Must line reached the market in 1976 as a lower-priced entry into the brand. Cartier made large numbers of Must watches in vermeil, so copies sit inside the same secondhand supply. Most fakes sell for $15 to $100. Genuine examples trade for $700 to $3,000, based on model, size and condition.
What the Must de Cartier line is
Cartier opened Les Must de Cartier boutiques in 1973. The Must de Cartier watch followed in 1976. Cases are 925 sterling silver with gold plating, a material called vermeil. Main models: Tank Must, Vendôme, and Must Vendôme Louis Cartier. Case widths run about 20 mm to 30 mm. Early pieces used mechanical movements. Later production used quartz.
Metal and hallmarks
Genuine Must watches carry marks on the outer caseback or inside it: “Argent 925,” “Plaque Or G 20M” or “OR G 20M,” plus a serial number. The code 20M states 20 microns of gold. US law sets the floor for vermeil at 2.5 microns of gold over sterling silver. Counterfeits use brass or steel with 1 to 2 microns of plating. Plating wears at the lugs and crown first. Weight is a fast test. A vermeil Tank Must weighs about 30 g to 45 g. A brass copy weighs less.
Movement
Cartier sourced Swiss quartz movements, ETA among them. A working quartz Must holds time to a few seconds per month after service. Copies use unbranded quartz modules. Holders are plastic or missing. Some cases hold a glued spacer instead of a metal ring.
Dial, crystal and crown
Genuine dials print Cartier in one typeface with a wide C. Fakes show uneven letter spacing, heavy serifs and a Swiss Made marker set in the wrong spot. Genuine crystals are sapphire. Many copies use mineral glass or acrylic, and both scratch. The crown holds a blue cabochon, a synthetic spinel, set flush with the metal. Fake cabochons sit high, use glass, or fall out.
Serial numbers
Genuine casebacks carry a number of 6 to 8 digits, stamped or engraved, plus a model reference. Numbers repeat across counterfeits because factories reuse one stamp. Cartier does not publish a public serial database. A number alone cannot confirm a watch. A Cartier boutique or a watchmaker with archive access can check a piece against service records.
Price tells
A Must de Cartier Tank at $50 is not a bargain. Counterfeit listings cluster at $15 to $100 on general marketplaces. Genuine vintage Must Tank vermeil watches sell for $700 to $3,000. The Vendôme line sits lower, near $500 to $1,500. Box, papers and service history move the number.
Legal note in the US
Selling a watch with a counterfeit Cartier mark violates the Lanham Act, 15 U.S.C. § 1114 and § 1125. US Customs can seize and destroy shipments under 19 U.S.C. § 1526. Cartier is owned by Richemont. The brand runs a trademark enforcement program, and resale platforms pull listings after rights-holder complaints.