A red octagonal sign means:

An octagonal (eight-sided) red sign always means STOP. You must come to a complete stop at the stop line if one is marked, or before the crosswalk, or before entering the intersection. After stopping, yield to all approaching traffic and pedestrians, then proceed when safe. Stop signs use a distinctive shape so they are recognizable even when partially obscured by snow, foliage, or vandalism — and from the back side, so drivers know an oncoming vehicle is approaching a stop. The shape and color of regulatory signs are standardized nationally under the MUTCD, so the octagonal red STOP sign means the same thing in every state. Rolling stops (slowing but not coming to a complete halt) are illegal and a common cause of tickets.