Sheffield Plate Pot- Marks?

Here is a what I believe is a Sheffield plate coffee/teapot that has a cross/globe mark for Blagden Hodgson c.1821, but it also has another mark, a divided square. Does anyone have an idea what this other mark is or means? Also, is this pot truly Sheffield Plate? Did Blagden Hodgson go on to make electroplate?

Any info much appreciated?

It certainly looks like Blagden, Hodgson & Co’s mark, but I can’t explain the square. If it is true OSP there may be somewhere around an edge where you can see the “sandwich” formation of the plate - this would be fairly conclusive. I don’t think Blagdens produced electroplate; I suspect they were probably taken over or superseded by another company before electroplating became popular.

Thank you so much for the info. The pot does indeed have the “sandwich” formation.
Thanks again!