I'm going with fliffy42 on this one. I believe this is a helper handle for a one man crosscut saw. Not the big two man saw like the lumberjack cartoons, but one that looks like a much heftier version of a carpenter's saw with a wooden grip (though usually without a top horn). The handle could be attached near the grip to allow two handed use, or at the end of the blade to allow another person to help make the cut. I couldn't find one that looked exactly like yours, but the general concept is the same. The one man saws had holes in the blade at each position, and the pin in your handle would go through these. The hook shaped part retains the pin. That's my guess and I'm sticking to it.
