There are 2 marks here. The first is a Chester import mark with the date letter H for the assay year 1908/9 and the sponsor's / importer's mark BM for Berthold Muller, a well-known importer of German silver. The second mark starting with the N is a Hanau silver mark of Neresheimer & Sons (see https://www.925-1000.com/Fgerman_hanau_marks_01.html).