Which geometric shape is commonly used for stop signs?
And the answer: octagon.
While the earliest stop signs were square-shaped, they've had the eight sides of an octagon since at least 1954. The unique shape helps drivers coming from the other direction, as well as those driving at night, to easily recognize the sign.
"Motor City," as Detroit, Michigan, would come to be known, was home to the very first stop sign. In the early 1900s, the design for the stop sign was very basic: a simple white square with "STOP" in black lettering.
As the 20th century progressed, however, the public appetite for the automobile grew insatiably. Coupled with a steep rise in the number of roadway construction projects, the need to establish a set of uniformed roadway signage standards became paramount.
Throughout the century, the design changed several times. Before its trademark red coloring, the stop sign was several variations of yellow and white. Finally, in 1954, it evolved into the design with which we're all familiar. This standard octagonal shape and red coloring has made its way around the world as a common roadside marker, finding its way from Egypt to France to Iran. In fact, stop sign usage became regulated at the UN Vienna Convention on Stop Signs during the Cold War (yes, we promise it's a real thing).