Cartier 18KT. Gold and Diamonds Tank Francaise Watch, stamped 18K and marked with serial number 1821, 299247MG., Cartier 18KT. Gold and Diamonds Tank Francaise Watch, stamped 18K and marked with serial number 1821, 299247MG., Cartier 18KT. Gold and Diamonds Tank Francaise Watch, stamped 18K and marked with serial number 1821, 299247MG.