Sheffield Tea Service screen with unusual mark..

[bafiv]

Hello, I am trying to identify the maker of this piece I've recently acquired and I've not had any luck. I am told that it is a Sheffield plate panel screen used to hide the waste bowl for a formal tea service or to act as a shield for the burner. It has a grape leaf motif around the edges of the panels and a crest in the center with a lion over a shield with a star/ Fleur de Lis/ crescent marking.I've been unable to locate any kind of confirmation that a tea screen is in fact what this piece was used for, what the mark on the back means, or that it's even English (and what time period of manufacture I'm dealing with). It's quite a mystery to me. Does anyone know anymore about what this piece is and who the maker is? In the middle of the center plate on the back is a mark which looks like the top of a flat head screw (an O with a line through it) with an upside down U joining the bottom of the circle. Towards the bottom of the plate is a character I'm pretty sure is the number seven. I'm assuming the north/south reading of the upper character is correct as I don't think you'd turn the piece on it's side to read the mark. Please see the attached images. Any information would be greatly appreciated.