I think it'd be pretty easy to tell the curvature of the fins. But as ChefJoe says, it is flowing from fan-hub to sticker side. So in the optional HD-Bay cage, the sticker is facing the motherboard.
However, on the side fan, it depends if you want intake or exhaust. I use it as an intake and get about ~7C cooler temperatures across my GFX cards. Others use it as exhaust and say they get better results. Try both ways and see.