Definitely looks like a vintage milling machine vise, lots of them were relegated to drill press duty when the Kurt Anglock type pretty much took over the market. If it is a B&S, it would most likely be stamped, often in very small letters, look at the top of the sliding jaw, especially that little flat pad right above where the screw goes in. Might have to wire wheel it, might be marked on top of the fixed jaw also, although I think somewhere on the sliding jaw is more likely.
HTH, Jim