SOS
The letters signified by the signal ( . . . — . . . ) prescribed by the International Radiotelegraphic Convention of 1908 for use by ships in distress.
SOS was chosen as the universal distress signal because this combination of three dots followed by three dashes followed by three dots (…—…), was easy to send and easily recognized, especially since they were usually sent as a nine-character signal, which stood out against the background of three-character Morse Code letters.
The letters themselves are meaningless. SOS does not stand for Save Our Souls, Save Our Ship, Stop Other Signals, or Sure Of Sinking.
Mws R Writings 