Book 25, Question 28
Why are stop signs red octagons?
A stop sign needs to be spotted fast, even from far away or from behind.
No other sign has eight sides, so the octagon shape is unique, and the red color means stop or danger. Because of its shape, you can recognize it even when snow covers its face. Different shapes mean different things: triangles warn about yielding, diamonds warn of hazards, and rectangles give information.