Upon further investigation, it appears that the reason that the C is still so bright is that initially, there would have been a raised C. You can see the four holes where the original C was attached. These holes go through to the back. This is why the brass underneath is still bright and preserved. Due to the orientation of the attach points on the back, I would say that it is a plate not a buckle. However, it has the shape of a snapped corner buckle and most of the plates that I have found online are oval. May be a unique piece!