I dug this yesterday and cannot figure out its purpose. So I've come to the panel of experts. Someone here will know what it is.
there appears to be a screw in the bottom hole, but it's still dirty in there and I can't tell for sure what it is. It does not look like a keyhole. The cut on the u-shaped top doesn't appear to have cut marks, but there is space for a saw blade to have been in there making a cut. The top "U" part does not swing around, so to separate at the "cut" it would need to be bent, which does not appear to ever have been. Pretty heavy for it's size. Dirt came off with a water only wash.
there appears to be a screw in the bottom hole, but it's still dirty in there and I can't tell for sure what it is. It does not look like a keyhole. The cut on the u-shaped top doesn't appear to have cut marks, but there is space for a saw blade to have been in there making a cut. The top "U" part does not swing around, so to separate at the "cut" it would need to be bent, which does not appear to ever have been. Pretty heavy for it's size. Dirt came off with a water only wash.