A distress signal used to notify danger or a ship/person in distress and request help; can be sent by radio, flags, lights, sounds, etc. (e.g., SOS).
夜間に船が救難信号を発し、沿岸警備隊が出動した。
At night the ship sent a distress signal and the coast guard was dispatched.
登山中に道に迷って携帯で救難信号を送った。
Lost while mountain climbing, I sent a distress signal with my phone.
緊急時には『SOS』という救難信号が国際的に通用する。
In emergencies, the distress signal 'SOS' is internationally recognized.