Decorative primitive wooden frame mold?

I got this at a garage/yard sale a while back and I have no idea what it is. The person selling it told me it was a mold for making decorative picture frames. It's definitely very old, heavy, and made of two types of wood. The lighter wood containing the actual design (which to me looks like grapes and leaves) can be removed from the "base". The whole thing measures 17.5" long, 5.5" wide, and about 2" high. There is what appears to be a maker's stamp on the edge of the lighter wood. It's marked "C Watson".

Does anyone know what this thing is or what it was used for?? Any help would be much appreciated! Thanks all!