But, it became the worldwide standard when it was included in the second International Radiographic Convention which was signed on November 3, 1906, and became effective from July 1, 1908.
In the past century, 'SOS' has become a firm part of popular culture used in everything from DIY programme titles to Abba hits, British newspaper 'The Times' reported.
But, it may be mentioned here that the call actually became famous when one of the radio operators of the ill-fated Titanic had supposedly said to his colleague: "Send SOS". The tragedy revealed just how vital a universal system was.
After the collision in April 1912, the ship's radio operators sent out both the old CQD and the new 'SOS' signals, but some ships in the area ignored both, thinking that they were having a party.
They soon learnt otherwise, as international headlines told how Jack Phillips, Titanic's first radio operator, and 1,500 others had been lost along with the "unsinkable" ship.
The new SOS distress signal was rarely ignored after that. Of course, technology has moved on dramatically since 1908 and only very occasionally are the telltale dots and dashes that have saved countless lives employed today.
So, it seems 'SOS' is safe for another century too!
