More than likely German. The skull is not an official SS or Third Reich symbol. Generally, the crossed bones are behind the jaw, and the vast majority of them have the skull tilted a bit to make it appear to be looking in a different direction. But a more common trait is the larger nose cavity (forgive my lack of anatomy language skills). It very well could be German from WWII, but I really doubt that it was in any way commissioned by the Nazis.
The sharpness of the lines and the shape of it would also indicate German to me. It would be an easy sell to a musician (us rock and rollers are known for our loud taste in jewelry haha) and many others I'm sure. The pictures aren't detailed enough for me to make an estimate on age though.
It very well could be Mexican and sold to tourists. But I've been down to Mexico enough times and it's too subtle to be a Rosarito special. The merchants at the stands prefer over sized skulls, iron crosses, and in generally, a lot more shine and polished look to them. I'm sticking with my theory that it's German.
