Old Pewter Plate with Hallmark

My mother in law had an awesome pewter collection at one time. Some of them were very old. I would like help learning about the hallmark on this piece. Strangely, the crown is on the top of the plate and not the bottom. And there is a mark next to it, perhaps a makers mark? The piece is heavy and has a wonderful patina. I have check out some sites for marks but I don't know if silver marks and pewter marks are one in the same. Anyone out there know about pewter markings? Much appreciated.