1A sign or signal transmitted to convey information, including technical signals such as electrical or radio signals; also used verbally as in 「信号を送る」("to send a signal").
衛星から地球へ信号が送られている。
Signals are being sent from the satellite to Earth.
船は霧の中で汽笛を信号として鳴らした。
The ship sounded its horn as a signal in the fog.
手を挙げて出発の信号を送った。
They raised their hand to signal the start.
無線機からノイズ混じりの信号が聞こえた。
A noisy signal came through the radio.
2A traffic light — the red/yellow/green signal used to control road traffic.
信号が赤に変わったので車を止めた。
I stopped the car because the light turned red.
この交差点は信号がなく、少し危ない。
This intersection doesn't have a traffic light, so it's a bit dangerous.
信号が青になるのを待ってから渡った。
I waited for the light to turn green before crossing.