Just found this post. I recently found this exact plate and posted it on Facebook only to find out that at least two other diggers have found them as well. This plate did have attachment points as seen from the backside of mine.
Communicating with the other two diggers, all three of us dug the plates in the SC Lowcountry at different locations but along with confederate and union buttons. We suspect that this may be a horse tack item. Sorry for the bad color on the backside shot but was taken with bad lighting.
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