CQD. Found this article by googling.
The first Radio Distress Signal was transmitted from the East Goodwin Lightship on 17 March 1899 when the merchant vessel Elbe ran aground on the Goodwin Sands. The message was received by the radio operator on duty at the South Foreland Lighthouse, who was able to summon the aid of the Ramsgate lifeboat.
The Goodwin Sands again featured in another 'first' when on 30 April 1899, the East Goodwin Sands Lightship sent a distress message on her own account when she was rammed by the SS R. F. Matthews. This was prior to the introduction of the 'SOS' and the recognised call sign for ships in distress then was 'CQD'. This signal had been devised by the Marconi Company, it was intended to mean 'All Stations - Urgent', but was popularly misinterpreted as 'Come Quick - Danger' or 'Come Quickly Down'.
The 'SOS' signal was established as an International Distress Signal by an agreement made between the British Marconi Society and the German Telefunk organisation at the Berlin Radio Conference, 3 October 1906. The signal was
formally introduced on 1 July 1908. The first time the 'SOS' signal was used in an emergency was on 10 June 1909, when the Cunard liner SS Slavonia was wrecked off the Azores. Two steamers received her signals and went to the rescue.