When the car became popular in the early 1900s, private groups rushed to place signs on popular roads to alert drivers to dangers and offer directions. This resulted in a wide range of signs with no standard shapes or colors. The first traffic sign standards came from the Mississippi Valley Association of Highway Departments in 1932. Today, there are hundreds of types of traffic signs in the United States.
Identify the shape of the sign. Some shapes are used for only one type of sign. Octagons are exclusively used for stop signs, circles for railroad-advance warning signs, X's for railroad crossings, equilateral triangles pointing down for yield signs and pennants for no-passing zones. Other shapes denote a category of signs. Diamonds are used for warning signs, rectangles with a longer vertical side are for regulatory signs, rectangles with a longer horizontal side are for guide signs and temporary traffic-control signs, and trapezoids are for national park and recreation signs. Pentagons are used for advance warning signs for schools and county route markers.
Identify the color of the sign's background. A black sign indicates a one-way street. Red means to slow down because it is only used on stop and yield signs. Orange is used for temporary traffic-control signs. Yellow is used on permanent warning signs including those posted near schools. Green is used for informative signs and to direct drivers to parking lots. Blue signs tell travelers where to find lodging, food and fuel. Brown is for parks, campsites and cultural attractions. White signs are regulatory signs.
Read the writing on the sign or look at the picture if the color or shape has not identified what it's trying to communicate. Most signs are easy to figure out based on the writing—for example, speed limit or "Do Not Enter" signs—or by graphics that warn against U-turns or direct drivers to merge.