Can someone help me with the date on this mug, and identify the manufacturer, please. The mug http://www.linbry.com/Tankard_general_view.jpg is about 4 1/2 inches high and 3 1/2 inches in diamter. The marks http://www.linbry.com/Tankard_hallmarks.jpg look to me like they are London, 1750, but I'm no...