Preheat broiler and set rack about 3 inches from heat source. Cut ham steak into 4 portions.
Stir syrup, mustard and vinegar in a small bowl to blend. Brush one side of ham steak liberally with syrup mixture and set on a foil-lined broiling pan. Broil until glaze is just speckled with golden brown spots and lightly bubbling, 5 to 7 minutes. Turn and brush other side of ham generously with syrup mixture. Broil until glaze is bubbly and speckled with golden brown spots, about 5 minutes longer.