An indication that a potentially bad or dangerous situation could develop.
A signal set at danger and showing a red light or other stop indication, which a train driver must not pass until it changes or until manually cleared past the signal by a dispatcher.
An indirect message or indication, especially concerning a future event.
A method of long-distance communication sometimes used in ancient and undeveloped societies, consisting of messages conveyed by means of columns or intermittent puffs of smoke.
A message or sign sent by this method.
A type of flare or combustion device sometimes used as a distress signal.