This is a screw on knob, so I’m guessing to a pan lid? It has the J M mark, and ocross from that what looks like a backwards 2. I’m wondering what the metal is?
To answer the question in the title of your post, yes other metals are marked, but, apart from precious metals such as gold and platinum, there are normally no accepted national or international standards.
I have no idea about your mark - it doesn’t look like any silver mark I have seen before.
I thought it must surely be from titanium or platinum cookware. I’ve looked all over online and can’t find anything. Of course I am hoping it is platinum, but it should have a platinum marking on it if so I’m guessing.