smoke signal

Short definition from Wiktionary

Noun

1. 1
   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.
2. 2
   A message or sign sent by this method.
3. 3
   An indirect message or indication, especially concerning a future event.
4. 4
   A type of flare or combustion device sometimes used as a distress signal.
5. 5
   Alternative spelling of smoke signal.