That contraption has a lot of moving parts!

Looks like it might rotate in two axes (360* around the handle, and ~180* left and right), as well as the jaw adjusting in and out with that wingnut. Strange. Never seen one before.
As for the marking, there are a few letters after the visible "CENT". Maybe "20th CENTURY". If you pull the jaw all the way out and clean it up you should be able to read it all.
EDIT:
Found it. It's a half of a brace wrench. Samuel Johnston patent 674,735 (1901). Made by P. Lowentraut. See DATAMP info on it linked
here.