What's the purpose of airline CREW tags?
It’s not an official/legal tag. Just a reminder for ground crew. At my company, luggage handlers unloading checked in luggage from the cargo will leave the bag near the aircraft (to be picked up by the crew) rather than bring it in to the terminal through the normal luggage flow. The ideea being that bag belongs to a crew member (active or positioning) and he might move arround the apron without ever going into the terminal.

Mind you this is just a courtesy, not a guaranteed thing. Should you put this on to your (checked in) bag there is a good posibility a ground operator will leave it under the plane for a while, then, when no crew comes to claim it, it will go through a lengthy process back to terminal. So your bag will have to honor of being one or two hours late to the conveyor belt.