How do you know if you have a Sapphire?

Written on the back of the case.

So it is!   Thanks,.  I wonder how the guy in the store knows, since it's not on the box? 

Only the steel version is without sapphire. I would say that there's a visible difference between the 2 materials and that it's easy to understand which one you're looking at...especially if you're doing it as a job.

Edit.

On the back of my box it's written "White titanium...." and titanium means sapphire glass. Not sure what's written on the back of the steel version.