I think usually the sticker applies to the bottom.. but .....
One trick you can try: if you have polarized sunglasses try putting them on and looking at the glass. If the glass is tempered you should see a checkerboard pattern. For example, look at your car windows with the polarized lenses, you should see the checkerboard pattern. This might help you determine whether it's OK to drill the sides.
FWIW, I have an 65g tank, it has the "do not drill" sticker on the bottom, and I was able to drill the back glass. I don't think it's Perfecto brand though, I think it might be AGA. Sooooooo... dunno if that really helps you.
The sunglasses trick might be worth a shot though ...