Cool whatever it is, but I think you might have it upside down. My only guess on the design would be a mitre. (common design on livery buttons) There's also misc. crowned things, usually using a fairly unofficial looking crown. I have seen a couple plates in the past with livery type designs, so that is where my guess would be. Not sure exactly what they were for, or how they were used, but they do exist.
Here's a thread to show what I'm talking about. Note the 2nd one shown... ""Don Troiani has id'd it as a personal coat of arms plate.c.1790-1810"
http://www.treasurenet.com/forums/t...-war-crossbelt-thurs-absolutely-stunning.html