This signal can be transmitted in various ways. It can be sent out as an audio tone, along a telephone wire as an electrical pulse, as long or short pulses of a radio signal, or as a visual signal by using a flash light, also it could be as simple as banging on something or making some kind of noise. It is codified as three dots, then three dashes and three dots again. This sequence is without any space between the dashes and dots. The three dots signify the letter S and the letter O is formed by three dashes.
(info on this I got from reading about it on other websites and magazines.)
There are various phrases that are used as a full form of SOS. They are as follows:
Save Our Souls, Save Our Ship, Send Out Sailors, Save Our Sailors, Stop Other Signals and Survivors On Ship.
"Sir, we're getting an faint S.O.S. signal from somewhere in our vicinity."
In the Netherlands it's also a slang term for cocaine.
radio operator: Yea don't sniff too much of that shit