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What's a "Remove Before Flight" ?

Initially it's a safety alert symbol placed at points that require an imperative control before all aircrafts take-off. In order to facilitate its location, it's usually made of long fabric or PVC red banner on which is inscribed REMOVE BEFORE FLIGHT.

Of course, it's essential that all be removed before the flight under penalty that the aircraft remains on the ground.
Generally, control is done by the pilot and his mechanic in charge of these checks. 

This object has quickly become a symbol of recognition for civilian or military pilots but also for aviation enthusiasts. The most common medium today is the keyring.