Y'all are on the right track. A globe sight was a front sight hood, which accepted interchangeable inserts. Regular post front sights could obscure distant targets, while the globe sight could be clear at the center. Circles of various configurations were used with open, or "peep" rear sights, so the target could be clearly sen. Sometimes a spirit level was used on the sight to make sure the weapon was held at a true vertical. See the link below. Stan