smoke signal
US /ˈsmoʊk ˌsɪɡ.nəl/
UK /ˈsmoʊk ˌsɪɡ.nəl/
1.
a column of smoke used as a signal, especially one made by a fire on a mountain or hill to send a message
:
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The stranded hikers sent up a smoke signal to alert rescuers.
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In ancient times, smoke signals were a common way to communicate over long distances.