Norges Gullsmedforbund, Oslo, Norway, c.1932 - present. NM stands for Norsk Monster which means the design is copyrighted or protected. GP stands for "Gullsmed Plett.
Hello. Believe that's JN for Jules Nordmann, 13 Hatton Garden, London. He entered this mark at Birmingham on February 8, 1882. It's not unusual for London watch case makers to enter marks at Chester and Birmingham. I read the "k" date mark as 1884. Watch cases were exempt from duty. A Brit...