This made the yellow signal difficult to notice.

In what consternation must the Kinyanpi have viewed the plethora of yellow signals beneath them.

Some timed train stops require the driver to acknowledge a stimulus before the trip arm is lowered on a yellow signal.

A courier was despatched on the strength of that yellow signal.

However, changes were made to the signalling at Eltham so that through trains would receive a yellow signal on approach.

In a second change announced today, each time engineers see a restrictive signal, red or yellow, they will be required to announce that fact aloud.

A yellow signal means the next signal will be red.

The ability to tell colors apart is crucial in a system where engineers must read red, yellow and green signals.

Picard stood and Rosario at tactical snapped on the yellow alert signal.

The yellow alert signal flashed ominously behind him, like a continuous warning that something terrible could go wrong any second.