Regulatory signs are usually rectangular, with the exception of the octagonal stop sign and triangular yield sign. Directional arrow signs such as signs forbidding left or right turns and Wrong Way signs are often square.
Regulatory signs inform drivers of traffic laws that may not be obvious. Signs dealing with vehicle speed, including speed limit, reduced speed and speed zone ahead signs are rectangular with black print on a white background. Regulatory signs forbidding left, right or U-turns are square with a transected red circle atop a black directional arrow on a white background. No Turns and Left Lane Must Turn Left show black text on a square white background. Do Not Pass and Pass With Care signs are rectangular with black text on a white background.
Signs instructing directionality include the One Way, Wrong Way and Do Not Enter signs. A One Way sign is either a long horizontal rectangular sign with black text inside a white arrow on a black background or a vertical rectangle with black text on a white background. Do Not Enter signs show white text on a red circle inside a white square and Wrong Way signs are horizontal rectangles with white text on a red background.