Good reading.... Could be København (Copenhagen)
I use a Dremel rotary tool with the #428 wire brush attachment to clean off the "age of time" corrosion. It often reveals back marks that are recessed / inscribed. Just be careful using it on the embossed/raised design, and know that it will take off some of the original surface. (I wouldn't use it on a button that still had any gilt on it).No :-( - Maybe if i find out, how to remove the "age-of time -in-the dirt"