#TIL stop signs shaped like octagons were invented in Mississippi in 1923 because someone thought that the more sides a shape had, the higher a danger level it invoked.
A triangle has the fewest number of sides, so it's just a warning.
A square has 4 sides, so it ups the warning level a little.
An octagon has 8 sides, so that's the warning that says Stop Right Where You Are Because Horrors Shall Ensue.

I'm assuming that if we ever see a >8-sided sign, it means #Cthulhu has arrived.