I have an all matching crispy purpose built model 38 short rifle with an unusual stock disc that I have never seen before. It is brass. It is in the usual spot on the stock and it is attached with 4 brass nails. On the stock is a large M over the number 28 over 3 swedish crowns. I wish I knew how to post a photo here but I dont. Does anyone know what this disc means? I can e mail anyone interested a photo of it. Thanks in advance.