Well any one that has ever used a nail set knows that little indent in the center of the nail shown, is where you put the tip !! That makes it a newer nail to me !! Looks like someone let the claw slip when trying to remove the nail !! Flat sides when that happens, then you turn the claw and try again and if it slips you get 4 flat sides !! My Grandad tore down old houses when building work was scarce !! I had to clean many of those boards !! As for the window itself,,,the one that Cogar posted is a much older window looking at the wedge shape mullion,, the one with the glass has a flat front,, no wedge !! That makes it newer to me !! And I think it would have been hung just as the pic shows,, wouldn`t hold water since the bottom is sloped as it should be to shed water !! But as with everything here,, its just one persons opinion !!
$100. is an excellent price but do more research first. Check around town or like I said ask at the local historical society !! Chances are this was a keepsake from a church that was being torn down or remodeled !! People are good at that !!