SOS
In contrast to CQD, which was sent as three separate letters with spaces between each letter, the SOS distress call has always been transmitted as a continuous sequence of dits-and-dahs, and not as individual letters. There was no problem as long as operators were aware that "SOS" was technically just a convenient way for remembering the proper sequence of the distress signal's total of nine dits and dahs. In later years, the number of special Morse symbols increased. In order to designate the proper sequence of dits-and-dahs for a long special symbol, the standard practice is to list alphabetic characters which contain the same dits-and-dahs in the same order, with a bar atop the character sequence to indicate that there should not be any internal spaces in the transmission. Thus, under the modern notation, the distress signal becomes SOS. (In International Morse, VTB, IJS and SMB, among others, would also correctly translate into the · · · — — — · · ·  distress call sequence, but traditionally only SOS is used).