Warning Signs
Warning signs tell you what is coming, not what you must do right now. They are overwhelmingly yellow diamonds with black symbols or words, and the exam tests whether you can decode the symbol, the advisory plaque beneath it, and the distance between the sign and the hazard. Fluorescent yellow-green marks pedestrian, school and bicycle warnings; orange marks work zones - a distinction the exam uses often.
What the major warnings mean
Curve signs (a black arrow bending left or right) warn of a turn ahead; a winding road sign shows a serpentine arrow. Chevron signs - large white arrows on a rectangle - are placed in the curve itself to show its direction. Intersection warnings include cross road, side road, T-intersection, roundabout ahead, and STOP AHEAD or YIELD AHEAD, which tell you a regulatory sign is coming. Condition warnings cover slippery when wet, steep grades (with a percentage), narrow bridge, lane ends, merge, divided highway begins or ends, and two-way traffic.
Advisory speeds are not limits
A yellow speed plaque under a curve sign, such as 30 MPH, is an advisory speed: the speed at which the curve can be driven comfortably under good conditions. The white SPEED LIMIT sign remains the legal maximum. On a wet or icy road the safe speed may be well below the advisory number, and 'too fast for conditions' can be charged even below the posted limit.
Railroad crossings
A round yellow sign with an X and 'RR' is an advance warning. The crossbuck at the tracks means yield to trains. Flashing red lights mean stop; lowered gates mean stop and stay stopped until the gates rise and the lights quit flashing.
Worked example
A road is posted 45 MPH. A curve sign carries a 30 MPH advisory plaque, and the pavement is wet. The driver should enter the curve at or below 30, not 45. The white sign sets the legal ceiling, the yellow plaque recommends a safe speed for the geometry, and rain lowers the safe speed further. Crash liability follows the safe speed, not the posted number.
Traps
Assuming an advisory plaque is enforceable as a limit (it is not, but exceeding a safe speed still can be); mistaking fluorescent yellow-green for standard warning yellow; and ignoring distance plaques or 'WHEN FLASHING' plates.