1) CD signal 2) Alert nullifier 3) Danger has passed signal 4) Kind of signal 5) Permission to proceed 6) Post-danger signal 7) Reassuring signal 8) Safe call 9) Safety announcement 10) Safety signal 11) Signal that danger has passed 12) Stand-down signal 13) The danger has passed 14) Welcome signal 
An all-clear is a signal used by civil defense or military authorities to inform others that an imminent physical danger has passed. ...
Signified by a siren at the end of a race, the all clear means that the stewards deem the finishing order of horses is correct and bets may be paid out. It also means that no protest or objection has been made by the connections of any horse in the race.
[n] - a signal (usually a siren) that danger is over 2. [n] - permission to proceed because obstacles have been removed
noun a signal (usually a siren) that danger is over
the signal that an air raid or other danger is over.