Stop signs first showed up in Detroit, Michigan, in 1915.
They were black on white and smaller than modern signs.
Until then traffic-control devices were generally manual, using semaphores, or flags, policemen in traffic towers, and hand-turned stop-and-go signs.
In the 1920s, black-on-yellow signs were introduced, while white on-red signs appeared in 1954.
Mounting height has also evolved.
Early stop signs were about three feet off the ground.
Modern stop signs are more than six feet high, making them easier to see.
