Road and Highway Signs

Traffic sign - wikipedia.org
Traffic signs or road signs are signs erected at the side of roads to provide information to road users. With traffic volumes increasing over the last eight decades, many countries have adopted pictorial signs or otherwise simplified and standardized their signs to facilitate international travel where language differences would create barriers, and in general to help enhance traffic safety. Such pictorial signs use symbols (often silhouettes) in place of words and are usually based on international protocols. Such signs were first developed in Europe, and have been adopted by most countries to varying degrees.
en.wikipedia.org/wiki/Traffic_sign
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Automobile and Driving Glossary - about.com
If you are a non-European planning to drive in Europe, you should make sure that you know what the traffic signs mean. Most European traffic signs are uniform throughout the continent and they usually communicate via symbols and graphics. But there are also situations where knowing German is important.
german.about.com/library/blauto_traf.htm

Brian's Guide to Getting Around Germany
A comprehensive guide of German traffic signs, signals, and markings. This guide is designed for both the short-term tourist wanting to learn German traffic signs in preparation for a trip as well as for someone who is studying to get a German or US military driver's license. This topic is divided into two pages. These pages may also be of interest to road and sign aficionados.
gettingaroundgermany.info/zeichen.shtml

Road Signs In The USA And Canada
Introduction - Colours, Shapes And Types Of Road Signs.
johncletheroe.org/usa_can/driving/signs.htm

Manual of Traffic Signs
This is a comprehensive listing of the most commonly used traffic signs in the United States.
trafficsign.us/
Standard Sign Shapes    Standard Sign Colors   

Traffic & Road Sign Test
Test your knowledge on the meanings of traffic and road signs. This test contains 5 parts, 30 multiple choice questions for each part. Grading is in real time after you submit the results and a detailed answer sheet is provided. Driving is a privilege, you are responsible for knowing what all traffic control signs mean.
usa-traffic-signs.com/Test_s/50.htm