Stop signs began appearing in various American cities in the 1910s. Both Blair, Nebraska and Detroit, Michigan introduced stop signs in 1915. Detroit also had the first three-color traffic signal, installed in 1920. In the early days, stop signs were not standardized, nor were they used everywhere. In the 1920s, national organizations began to standardize the use and appearance of stop signs, and the white-on-red version used today was not introduced until 1954.
The first national group to create rules regarding stop signs, the American Association of State Highway Officials (AASHO), convened in 1922 and developed the octagonal shape as the standard. At this time, stop signs had the word STOP painted in black on a white background. The First National Conference on Street and Highway Safety (NCSHS) came up with a number of ideas regarding shapes and colors for different types of street signs in 1924, one of which was the white-on-red stop sign. However, AASHO adopted black letters on a yellow background as the stop sign standard the same year, as the combination was shown to have the best visibility. This style of stop sign, mounted two or three feet (0.6 to 0.9 m) off the ground, remained the standard until 1954.
AASHO and NCSHS merged into a single entity in 1935 and published the Manual on Uniform Traffic Control Devices for Streets and Highways (MUTCD). They continued to publish updated versions through 1971, and the organization still exists today. In 1954, due to improved reflective paints, the white-on-red stop sign finally replaced the black-on-yellow version. In 1966, following MUTCD standards became a national law. The latest MUTCD, published in 1971, stipulated that stop signs be posted seven feet (2.1 m) above the ground.
Other countries have used various styles of stop signs through the years. Recently, the European Union adopted the United States style of stop sign as part of their efforts at standardization. Other countries around the world have stop signs following the United States model, often with the word STOP in the local language. Thailand, China, Hong Kong, Taiwan, French Canada, and most Central and South American countries have stop signs that follow MUTCD guidelines in every particular except for language.