If you look at the fan and u see the cable and those 4 things that hold the fan thats the way the air will be blowing out. Like here http://benchmarkreviews.com/images/...hermaltake_spedo_advance_backside_cpu_fan.jpg
Right, almost all fans blow toward the fan motor braces.
But really looking at the blades you can tell which way they blow.
You can tell which way it turns by the way the blades are curved, which in turn tells you which way it blows. It would not make any sense to curve the blades one way and turn it the other way, it would not move hardly any air.Not if you don't know which way the blade turns.