I’m an italian collector of wristwatches and I’ve recently purchased an old watch with a sterling case.

On the inside caseback there are some marks that I’d like to identify.


I know that the triangle is the import mark of Birmingham, but what about the “GS” mark? And the “S” is for 1917 or what else?
Moreover on the buckle there are some more marks that I can’t identify.


Could you help me?
Many thanks