SOS is a signal that stands for save our ship. An SOS signal would be sent out over the telegraphs or other communication system on a vehicle. Saying the letters SOS would not be confusing to anyone. They would immediately recognize what the ship is trying to say. It is easy to say and it can be said quickly. Usually in these situations, it is an emergency and the people are panicking. So, many people would immediately know what the ship is wanting.
SOS is an international message so any ship would know what that means despite speaking a different language. SOS can be sent over a wireless machine by the distress signal being three short dots followed by three long dashes and then three short dots.
