screwback lapel pin "SAM"

I found this pin in a jar of buttons that were given to me by my great grandmother. I know between my receiving it and her death at least 20 years have passed. I'd like to assume that one of my great grandparents belonged to this organization but I can't be sure.

The pin is just over 1 cm in diameter, and has a screw-back post that is about 3mm in diameter.

The back of the pin & the screw-back wheel are stamped "sterling". I've not been able to find any other type of makers-mark.

I attempted to contact the organization it would have been issued through, and they told me only "that's our old pin, its made of silver, we use a different one now" I do know the organization was founded in 1912. I would love to learn more about pins of this style, maybe even when it was made and if its worth anything.