Unidentified

I bought a bangle secondhand on eBay and surprisingly it came from an address within easy walking distance of my house!

It's marked 925 Sterling silver and has a mark that suggests it was imported to Sheffield. The makers mark is GM inside a rectangle (not GM & co) and that's where the mystery starts. I've been through lists of British hallmarks to no avail (but then why would the maker be from Britain if it was imported?) the item looks Scandinavian or Danish but I'm having no joy with the makers mark. There is another stamp on it too which is the astrological symbol for Libra, a straight horizontal line at the bottom and a curved 'hump' line above. I am stumped!