Air traffic control towers always have windows that slope toward the tower at the base. Many people assume they are designed that way to prevent the sun's reflection or glare from blinding incoming pilots.
The benefit is not for those outside the tower, but those inside it. Ordinarily, we see reflections in glass all the time, for example from computer monitors or car windows, but air traffic controllers must not have any distracting reflections as they monitor flights. By tilting the glass away, any light from inside the tower (such as video screens, lights, etc.) are reflected up onto the ceiling, which is painted black. That way, the glow from a wristwatch across the room won't be mistaken for an incoming UFO.