I ran across this tip after spending about an hour getting spotted by the guards on the walkway above the two platforms on Train Station (Run for Your Life chapter).
"Not being seen on this level is hell. To ease matters, it pays to learn the attention-avoiding spin. Basically, if someone is looking at you and you’re about to be spotted, you turn your back to them to stop it from happening, but here, commonly, as you make your way across the station platforms, you will be getting attention from many sides at once, especially on the more difficult settings.
You can avoid this by spinning once all the way around, taking a step in the direction you need to go, then repeating. Works like a charm at all difficulty levels."
Also, if you are trying to blend in with the crowd, try standing still, it seems to work better that way.