What is a 'Safety Signal'?

A safety signal is a message concerned with the safety of ships/vehicles indicating a meteorological warning (e.g. storm), danger to navigation warning or other navigational-aid message. Safety Signal is an important message because a delay in its transmission or reception can bring a disaster.

In radio telegraphy, it consists of the three repetitions of the group TTT ( _ _ _ ) sent slowly followed by the station call-sign. Letters of each successive group should be clearly separated from each other.