The earliest traffic signals did not consist of the tri-colored light system we use today. Rather, the semaphore signal was operated, either manually or automatically, at busy intersections. Garrett Morgan, an African-American inventor, is credited with patenting, in 1923, the first semaphore traffic signal, which consisted of a mechanical device that rotated "Stop" or "Go" flags for the approaching traffic. Originally, police officers were assigned the duty of holding traffic flags, but Garrett's new invention, seen in the image below, provided a hand-crank for rotating the flags. As can be seen on the left, the flags have been lowered in the "Stop" position, while the traffic coming from the other direction has the "Go" sign. In the center image, the flags are raised for all traffic to stop and allow pedestrians to safely cross the road. The image on the right is another more ornate example of a semaphore signal. Many semaphore signals featured lights and bells for added safety. Bells would ring when the semaphore signals were changing to alert drivers. Red or green lights were also added to the flags for easier visibility. The semaphore signal was used until the four-way, tri-colored light signal became the standard in 1935.