You can take a traffic and road sign test for free online at the DMV.org and USA-Traffic-Signs.com websites. Both sites provide online tests, but DMV.org also offers links to fee-based tests that are customized to the particular state of the driver.
The test on the USA-Traffic-Signs.com website is broken into five parts and focuses on a wide variety of traffic and road signs, such as "no U-Turn," "crosswalk" and "slippery when wet." The site also scores your results after you have taken the test to help you achieve the minimum score necessary on most official tests by state departments of motor vehicles. The site also offers the average, median and mean scores for the five parts of the test.
Comparatively, the DMV.org test is much simpler, offering seven traffic and road sign questions that are meant to be adequate practice for what is included on an official state exam. This practice test is multiple choice, and each question has four possible answers. In addition to offering links to more thorough tests, the DMV.org website offers other helpful practice exams, such as practice permit and driver's license exam tests as well as resources to help you locate and contact your local DMV office.