I have never seen a window latch that has a base like that. They are generally open based on the strike side. Additionally, there are no signs of countersink tapers that would accommodate wood screws. I am wondering though if your relic is upside down in the photos, and if so, if it isn't a bracket off the side of an old bucket, pot, pan, or something of that nature to which a handle was attached to? The three rivets would be where it was riveted to the vessel. It also appears as though there is wear on both sides of the center nub that would be consistent with the bail bracket theory.