Smoke signal

A smoke signal was a primitive form of visual communication which utilized puffs of smoke to communicate over long distances.

In 2151, after discovering a Minshara class planet, Captain Archer recommended against hailing the planet inhabitants as he was unsure if they were using "high-band frequencies or smoke signals". 

In 2373, after being stranded on the abandoned Cardassian space station Empok Nor with no working subspace transceiver, Crewman Amaro sarcastically recommended to Chief O'Brien that they send out smoke signals to call for help. This comment gave O'Brien the idea of using the station's deflector grid to emit a series of covariant pulses like an old-fashioned telegraph and send out an SOS.