A signal of distress is a message used to communicate that someone is in urgent need of help. There are various synonyms for this phrase, including SOS which is derived from the Morse code, Mayday which is used in aviation and maritime emergency situations, and Pan-Pan which is used to indicate an urgent but non-life-threatening situation. Other synonyms include emergency signal, distress call, distress signal, and alarm signal. These signals can be communicated through various means such as radio, flags, flares, and smoke. Regardless of the synonym used, it is important to recognize and respond promptly to any signal of distress to ensure the safety of those in need.