I thought that, if anyone who still wants to know the answer, it follows below ...
Clues by those who knew the answer (or have learned it) were starting to show up all over the place (remorse, S & O, transmitted, Message In A Bottle lyrics at end of verse (SOS repeated) and title of ABBA song (SOS).
For people that are still battling with their brain, the characters come from the International Morse Code in ascending order of "dots" or "dashes"
Thus ...
"SOS" =
Originally, SOS did not actually stand for anything (e.g. "Save Our Souls"). It was used since the letters S and O are easy to make and are distinctive.