If the ham comes with the skin still attached, remove most of it with a sharp knife, leaving a layer of fat and a collar of skin around the shank bone. Trim the fat, leaving a layer about 1/3 inch thick, and score the layer remaining into diamonds. Bake the ham on a rack in a roasting pan in a preheated 350°F. oven for 55 minutes. In a blender blend together the ginger, the brown sugar, and the rum, spoon the glaze over the ham, spreading it, and bake the ham for 30 to 35 minutes more, or until the glaze is brown and bubbly. Transfer the ham to a platter, garnish the platter with the parsley, and let the ham stand for 15 minutes before carving.