Antique half pint copper tankard / measure from 1820’s. The symbols above the engraving 1/2 PINT show a crown above GR above 6. My research indicates this is a formal stamp applied by the weights and measures inspector in Hertford under the authority granted to him by George 1V, who died in June 1830. The inspector using the number 6 operated between 1825 and 1860. I am not an expert on this so make no representation.