We usually read text looking straight at it. If you pick up a magazine or read a screen it is more-or-less at a 90-degree angle to your eye-line. However, sometimes a designer knows readers will look from another angle. The lettering has to look right from this viewpoint with anamorphosis [topic 1].
The lettering ‘SLOW ARAF’ ‘BUS’ or ‘STOP’ written on roads is an example of anamorphic design. The letters are very tall so that you can read them at an oblique angle from far down the road in a car. If the car is going fast, the driver needs to read the warning from further away.