SOS
This was announced on January 7, 1904 by "Circular 57" of the Marconi International Marine Communication Company. It became effective for Marconi installations on February 1, 1904. Another suggestion appeared in the 1906 edition of S. S. Robison's "Manual of Wireless Telegraphy for the Use of Naval Electricians," published for use by the United States Navy. This stated that the standard visual flag signals, known as the International Code of Signals, would likely also be adopted for radio use. Therefore, the flag signal "NC" ( — ·     — · — · ), which stood for "In distress; want immediate assistance", would also likely become the radio distress call.