They are stamps that look like hallmarks. It's English electro plate. The B is the quality letter. The best quality was "A1" or "AI", lower level was "A", next level was "B", followed by level "C", and the lowest level was "D". I think the JG over EP says it was made by Joseph Gilbert, Birmingham, England. It's pre-1890 which was when putting silver hallmark-looking stamps on silver plate became illegal in Britain.
Similar marks here in this question from 2006. You might get a more detailed answer if you join that forum.