When you encounter an octagonal (eight-sided) sign, you must

This is, of course, a stop sign, the only type of sign that has an octagonal (eight-sided) shape. A stop sign has the word "STOP" printed in white on a red background. It is usually found at intersections. At a stop sign, you must stop before the stop line or crosswalk if any. Then yield to pedestrians and other vehicles, and proceed only when it is safe to do so.