Speed Limit sign
The maximum legal speed in ideal conditions on this stretch of road.
How to recognise it
This sign is a tall rectangle in white, the standard background for a rule you must obey. These carry the force of law. Ignore one and you have broken a traffic rule, not just a guideline. Most are white rectangles with black text, and the handful that are not, the stop and yield signs, get their own unmistakable shapes.
What the test wants you to know
The number is a ceiling, not a target. Every state also has a basic speed law requiring you to drive slower when rain, fog, traffic or darkness make the posted limit unsafe, and that is the answer tests are usually fishing for.
Practise it
Reading about a sign is not the same as recognising it in half a second with an examiner watching. Every state road signs test on this site shows the sign and asks you to name it, then shows four faces and asks you to pick the right one.
Stop
Yield
Do Not Enter
Wrong Way
One Way
No U Turn