A stop sign has eight sides. The word “stop” appears in white reflective letters on a red background with a white reflective border. The minimum size of a stop sign is 30 inches by 30 inches.
While the current specifications for stop signs are spelled out in the "Manual on Uniform Traffic Control Devices for Streets and Highways," the shape of traffic signs, including stop signs, was determined by the Mississippi Valley Association of State Highway Departments in 1923. The association recommended that the more sides a sign had, the higher the level of danger it indicated. A round sign, considered to have an infinite number of sides, indicated the highest level of danger and was recommended for railroad crossings. The octagonal shape, the next highest danger level, was assigned to the stop sign. Diamond-shaped signs were used for warning signs, and square and rectangular signs provided information.