With this multiplayer mod, users may take the keys out of a car so that other players can't drive it.
Only the key holder will be able to "tab" vehicles that have had their keys removed.
ALT + E is one of the key bindings that can be changed in the controls screen.
– Game Settings Max. Keys: Determines how many car keys a player is allowed to own (Limit = 60).
Master Key: When the key owner is not online, admin users may have direct access to other user cars from the same farm.
– Restore Keys: Regardless of the user, this function returns the keys to the vehicle that is now in use. If no vehicle is entered, all car keys are returned, regardless of the user.
Note: This mod will not work in single player mode and is only intended for multiplayer games.

Thanks to GtX