Oh. Interesting. Wonder what the story was, there? This particular Queen Mary was the wife of George V, if I'm not mistaken, which would put this somewhere circa 1910-36, I suppose.
Not sure what the story was behind it or how it survived for so long as was found in with my late grandfather's military things it's the thickness of a pound coin and there is nothing on the back I'm not sure if there ever was Sent from my SM-G935F using Tapatalk