Studies have shown that our eye/brain connection registers different responses to different shapes-at first I thought that might be why there are so few octagon shapes in our surroundings-that the eye/brain connection deemed that shape less desireable. But, really octagons are everywhere and supports the notion that we generally favor lines that show some curve or flow. Here are a few things I found:
On that note we will STOP, except to say that did you know the first STOP sign appeared in Michigan in 1915? Originally yellow with black lettering, the stop sign is now recognized everywhere. A Vienna Convention on Road Signs and Signals in 1968 established guidelines for designs with two types of stops signs and three acceptable alternatives. Wikipedia has an entire gallery of stops signs around the world.
The next time you pull up to a stop sign, know that someone planned that!