A curious collar. (and it is a collar badge). I have a few facing pairs in this pattern, white metal and silver plate, lugged and pinback. However, all of mine are fully struck on the back, not solid as in this example?
I think the mark on the back is a 'national' mark. A government hallmark which is a C with a lion's head in the middle.
"THE NATIONAL MARK
In 1934 the Government of Canada instituted a national mark for items made of precious metal that are wholly manufactured in Canada. The mark was a lion’s head inside a letter C. (It was changed to a maple leaf inside a letter C in 1978.)"
http://justinteeantiques.com/news-in...-20th-century/