A button that seems to be a maker's mark makes it VERY interesting. In my experience, it means it is a hand-made button, expensive in its time, and reserved for the wealthy ones. The button seems to have some oxidation issues. That may mean that the design (if present) has been "replaced" with a type of corrosion. If you remove the corrosion, much of the detail may also come off. Whatever you use to try and clean the button, I would suggest you try small areas on the back to see how the surface reacts. If you find a cleaner that works, slowly expand the area you clean. I think this one may be worth a lot of time and effort.
Daryl