Traffic signs have specific shapes and colors that denote specific meaning. These shapes and colors allow you to quickly determine whether you are being presented with:
- Regulation
- Warning
- Information or guidance
Shapes
The octagon-shaped sign is used exclusively for stop signs.
An equilateral triangle shaped sign pointed down means YIELD to other vehicles and pedestrians.
The shape of a circle is used for railroad advance warnings and civil defense evacuation route markers. This sign is most commonly used in California for advance warning that means there is a railroad crossing ahead.
This shape of a crossbuck is used exclusively to warn of a railroad crossing.
This shape is used exclusively to indicate a school zone or a school crossing. A driver should be able to immediately recognize that a sign in the shape of a pentagon means that you should watch for children in or around the roadway.
The shape of a diamond sign is used exclusively for warning signs (e.g., cross road ahead, end/begin divided road, merging traffic, curves and construction warning signs). This sign indicates that there is a potentially dangerous situation ahead or some change in roadway conditions ahead.
This sideways, elongated triangle is used as a warning sign. This sign may also have the words NO PASSING inside the triangle. When a driver sees this yellow and black sign, he or she should not attempt to pass (the lines on the road will also indicate a no-passing area).
The shape of a vertical rectangle is used for regulatory (e.g., speed limit, no parking, carpool, and keep right) and sometimes warning (e.g., slow- children at play) signs.
The square shape sign is used for regulatory (e.g., do not enter, no U turn, no parking, no pedestrian crossing), warning (e.g., advisory speed limit and construction) and guide (camping and airport) signs.
The shape of horizontal rectangle is used for regulatory (e.g., road closed and carpool), warning (e.g., signal or stop ahead) and guide (e.g., rest area ahead and construction) signs.
Colors
BLACK is used as background for ONE WAY, night speed limit (in other states) and truck regulatory signs. It is also used as a legend color on signs with white, orange and fluorescent yellow-green backgrounds.
RED is used exclusively for:
STOP and YIELD signs- Multi-way supplemental plates (e.g., 4-way stop)
- DO NOT ENTER and WRONG WAY signs
- For legend or symbols on certain regulatory signs
- Part of Interstate and certain State route Markers
A red circle with a red line through it is also used to denote that something is not permitted. The picture inside the circle 
shows what you cannot do.
WHITE is used as background for route markers, guide signs and certain regulatory signs. It also used as a legend color on 
signs with brown, green, blue, black and red backgrounds.
ORANGE is used as background color for construction and maintenance signs.
YELLOW is used as background color for warning signs (except construction and maintenance signs), and some school signs.
BROWN is used as background color for guide and information signs related to points of recreational or cultural interest and on some street name signs.
GREEN is used as background color for guide signs, mileposts and street name signs. It is also used a as legend color
on permissive regulation and parking signs.
BLUE is used as background color for traveler services information signs, Civil Defense Evacuation Route Markers and some street name signs.
