Sail races are governed with flags and sound signals to indicate flag changes. The flags used are taken from the International maritime signal flag set. During a race and for any signal concerning the race, these flags are defined in the ISAF Racing Rules of Sailing but the signal can be modified by the Sailing Instructions.
The raising (hoisting) or removing of a visual signal is accompanied by the emission of a sound signal to draw attention to the new signal. The type of the sound signal (one short sound, two short sounds, one long sound, etc.) is described by the rule according to the type of signal.