Why do "STOP" signs have eight sides?

(...) in 1923, a branch of Mississippi's highway department suggested a change-what if a sign's shape could denote the kind of hazard ahead? The logic was simple: The more sides a sign has, the more dangerous the upcoming stretch of road is. Circles (which were considered to have infinite sides) designated the riskiest hazards, like railroad crossings. Octagons denoted the second most perilous hazards, like intersections. Diamonds signaled less-tricky stretches, and rectangles were strictly informational.