Pendant / Brooch Signed

I think I got the camera to cooperate, so I just edited and put better photos up...finally!!!

This Butterfly can be used as a pendant or Brooch. It's also heavy at 28 grams and measures 2.5" wide x 2" tall.

I believe this Butterfly is Native American, Navajo with Red Coral and Turquoise inlay. But, I'm not positive...Could this be Mexican made???

There are Initials at the bottom..."SD"

Now what I do know is that William Singer did sign his name SD and he also used the inlay technique. But I really need to be positive.

I would really, really appreciate any help I can get here. I know some of you have books on Mexican Silver...I just don't want to misrepresent myself.

Thanks for your help!
Sue