George III (1760-1820), Mexico City dollar. Oval countermark upon Spanish eight reales of King Charles III (1759-88), 1778 FF, Mexico City mint, Mexico. Small oval hallmark of George III right at centre of obverse, bust of Spanish King laureate and draped right, date below, legend and toothed border surrounding. S. 3765A. Coin Good Very Fine, Counterstamp Good Very Fine.