What sign indicates facial drooping in a person when using the FAST acronym?

The sign that indicates facial drooping when using the FAST acronym is asking the person to smile. This is a critical component in identifying a possible stroke. When a person attempts to smile, facial drooping will manifest on one side of the face if a stroke is present. This is because a stroke can weaken the muscles on one side, leading to an asymmetrical smile. Recognizing this sign is vital for timely medical intervention.

The other options do not effectively assess for facial drooping. For instance, asking someone to nod or blink does not provide an indication of facial muscle control. Similarly, asking someone to open their mouth does not target the symmetry of facial muscles in the same way that a smile would. Therefore, utilizing the smile test is essential in the FAST acronym for early detection of strokes.