SOS
In both the April 1, 1905 German law, and the 1906 International regulations, the distress signal was specified as a continuous Morse code sequence of three-dits/three-dahs/three-dits, with no mention of any alphabetic equivalents. However, in International Morse three dits make the letter S, and three dahs the letter O, and it soon became common to refer to the distress signal as "SOS." An early report on "The International Radio-Telegraphic Convention" in the January 12, 1907 Electrical World said that "Vessels in distress use the special signal, SOS, repeated at short intervals." (In American Morse code, which was used by many coastal ships in the United States through the first part of the twentieth century, three dahs stood for the numeral "5", so in a few cases the distress signal was informally referred to as "S5S").