Help is urgently needed, but for whatever reason you're unable to speak or to be heard. The reason could be as simple as laryngitis or as serious as a stroke, as minor as being stuck out in the middle of a lake and needing gas or as significant as being buried in rubble after an earthquake. How do you call for help for yourself or someone else in situations like these?
Morse Code has been around for over 150 years. Its collection of dots and dashes to represent letters and numbers still has a place in communication among all of our modern cell phones and internet connections. While it can be a little tricky to learn the entire coded alphabet, its most recognizable phrase is the call for help: SOS. The easy to remember dot-dot-dot-dash-dash-dash-dot-dot-dot (... _ _ _ ...) of the Morse Code SOS is known not only by airplane pilots, amateur radio enthusiasts and military historians but also by the public, whose only contact with an SOS signal may have been a TV show or movie that used it. Because of its wide exposure to mainstream culture, the connection between using the SOS and the need for help has been made.
SOS: we know it when we see it, we know it when we hear it, and we don't need telegraphy equipment to send it. A shiny object catching the light, a tapping on a metal pipe, the switching on and off of a lamp or flashlight, or a fingernail clicked on the mouthpiece of a phone are just a few examples for sending out this distress signal. It's that sequence of flashes or sounds repeated over and over that makes folks first pay attention and then recognize that someone needs assistance.
Three quick taps or flashes, three slower ones, then three quick ones, tapped or sounded repeatedly: SOS. It's a simple, yet powerful call for help recognized the world over. Even if the sender gets it backwards and puts dashes where dots should be, the message will still get across that someone needs help and needs it now.