http://didyouknowfacts.com/stop-signs-8-sides/?utm_source=Web&utm_medium=Partner&utm_campaign=AOLHP&utm_term=pubexchange-did_you_know-aol
Developed by Missiissppi Highesy Dept in 1923. Shape denotes risk level. Highest to lowest : circle, octagon, diamond, rectangle.
I tried to sell my two cents worth, but no one would give me a plug nickel for it.
I don't have a leg to stand on.