Which color signal indicates that pedestrians should not cross?

Answer: C — Red.

The signal color that indicates pedestrians should not cross is red. In traffic signal systems, a red signal is universally recognized as a clear indication that movement must stop. For pedestrians, a red signal means they should not enter the crosswalk or intersection. This is critical for ensuring their safety, as crossing during a red phase can put them at risk of accidents with vehicles that are legally allowed to proceed. While green signals indicate that pedestrians may cross, and yellow signals serve as a warning that the light is about to change (and thus may not be a safe time to cross), the blue signal is not a standard traffic light color for regulating pedestrian movement. Therefore, red is the correct answer because it directly corresponds to the instruction for pedestrians to remain where they are and not proceed into the intersection.