What does a blue signal indicate regarding rolling equipment on tracks?

A blue signal is an important safety device used in rail operations. It specifically signifies that work is being performed by personnel on or near the tracks, which alerts train crews and others to exercise caution. The presence of a blue signal indicates that workers are in a potentially hazardous situation, and therefore, operational protocols must be followed to ensure their safety. This means that no one should move any rolling equipment onto the track where the blue signal is posted without specific authorization.

The other options do not align with the established meaning of a blue signal. For instance, a blue signal does not allow rolling equipment to enter the track, nor does it indicate that the track is clear for movement. Additionally, it does not serve as a warning of a moving train; rather, it's meant to protect workers on the track by ensuring that trains do not move into areas where personnel are present. Understanding the significance of blue signals is crucial for ensuring safety in rail operations.