On January 20 , 1914 , the London International Convention on Safety of Life at Sea adopted the Morse code signal TTT ( â '' â '' â '' ) , three letter T 's ( â '' ) spaced correctly as three letters so as not to be confused with the letter O ( - - - ) , as the `` Safety Signal , '' used for messages to ships `` involving safety of navigation and being of an urgent character . '' On January 20 , 1914 , the London International Convention on Safety of Life at Sea adopted the Morse code signal TTT ( â '' â '' â '' ) , three letter T 's ( â '' ) spaced correctly as three letters so as not to be confused with the letter O ( â '' â '' â '' ) , as the `` Safety Signal , '' used for messages to ships `` involving safety of navigation and being of an urgent character . ''