Drop some water onto the glass face, and jostle the item around a bit. If the water stays put in a semi-uniform droplet, regardless of the motion and angle, it's probably sapphire.
It's interesting what they're doing in terms of shapes beyond sheets and simple "lens" type constructions. I made a foolish watch purchase because the sapphire case back was especially compelling. (This isn't my video, but it's the same watch: http://www.youtube.com/watch?v=DxNgAXDDTgo)
I've wanted a camera lens made of sapphire front and rear elements, but the refraction index would require more custom engineering than it would be worth. Definitely more expensive than a few $10 UV filters. :-)
Only one watches have small blemish after drop of hot metal dropped on it while I was welding exhaust turbo manifold for my car. And even this one is tiny and adds nice touch to my watches :)