I found this Medical badge thingy this year and was wondering if anyone can date it to a decade and if they know if it was a pin or badge of some sort.. Stamped under U.S. is : 64MD3....so I was thinking the "64" might be 1964....but it would be much better if it meant 1864. Was found on a mid 1800's property. In the hole in the back is some type of fabric that has rotted away, but is still along the edge of the circle. Any help is appreciated !!