Thanks for the comments, folks.
Christine: I realise that this isn't in any of the documented Bagley stuff, but I found this at a car boot not far from Pontefract, and the star reminded me (however slightly) of the Bagley fish scale plate.
Tiger: Haven't found anything along those lines. There is a five-pointed star on Leerdam piece, but that's all.
Today someone suggested it might be American, but that's way out of my comfort zone.