What signal indicates an "emergency stop"?

The signal indicating an "emergency stop" is recognized as both arms raised above the head with palms facing forward. This signal is designed to be highly visible and unmistakable in emergency situations, ensuring that operators or workers on site can promptly and safely halt any machinery or operations.

Using both arms raised provides a clear and significant visual cue, making it effective even from a distance or amidst noisy environments where verbal communication may be hindered. The specific positioning of the palms facing forward further emphasizes the urgency of the signal, making it easily distinguishable from other hand signals that might be used in a construction or rigging context.

Other options, while they may communicate messages within the context of signaling, do not convey an emergency stop as clearly or effectively as the designated two-arm signal with palms forward.