Sign Colors, Shapes, and Symbols
Sign color and shape are shortcuts to meaning, and exam questions love to test them in isolation. Shape first: the octagon is reserved for STOP; the downward-pointing triangle for YIELD; the diamond for warning; the horizontal rectangle for guide or regulatory messages; the vertical rectangle for regulatory commands; the pentagon for school zones and crossings; the circle for railroad advance warnings; and the crossbuck (X-shaped) for the railroad crossing itself. A round yellow sign with a black X and "RR" is an advance railroad warning; a white X-shaped crossbuck with "RAILROAD CROSSING" marks the tracks.
Color second: red means stop, yield, or prohibit; white means regulatory; yellow means warning; orange means construction; green means guide and destinations; blue means motorist services; brown means recreation and culture; fluorescent yellow-green means school and pedestrian; and purple marks electronic toll collection lanes. Symbols carry meaning without words: a red circle with a slash prohibits, a curved arrow shows a turn, a pedestrian figure marks a crossing, and a deer or moose silhouette warns of animals.
Traps: mixing up the pentagon (school) with the diamond (warning); assuming any yellow sign is regulatory; confusing the round railroad advance sign with the crossbuck at the tracks; and forgetting that purple is toll-related. Worked example: a question describes a downward-pointing triangle with a red border. Shape and color together identify YIELD; the words are almost incidental.