Navajo markings

I am looking at a ring to buy but not sure if it is really old navajo as that is how it is being presented to me. The stone does look authentic. It has turned a very nice shade of green, however it has a crack acossed it. The markings say STERLING and then the mark of an arrow through a triangle. Sound familiar to any one?

Can you provide a link to the ring our a picture, thanks for sharing