Keychain - "Remove Before Flight"

You see them all the time on backpacks and luggage, REMOVE BEFORE FLIGHT.  But what do they mean? 

Remove before flight is a safety warning often seen on removable aircraft components, typically in the form of a red ribbon, to indicate that a device, such as a protective cover or a pin to prevent the movement of mechanical parts, is only used when the aircraft is on the ground.  Other ribbons labelled "pull to arm" or similar are found on missiles and other weapon systems that are not mounted on aircraft.

Remove-before-flight components are often referred to as "red tag items". Typically, the ground crew will have a checklist of remove-before-flight items. Some checklists will require the ribbon or tag to be attached to the checklist to verify it has been removed.