Well, this could be possible, with the use of sounds and light flashing. Maybe every second or two, make the lights toggle on or off, based on their previous state, and make a horn sound play for anybody in range.
EDIT: I think the onVehicleUpdate() callback checks for the movement when unoccupied, and detects what player moved it ... You could use this for an alarm system in the meantime. I gotta check the LU Bible (Wiki) for this however, so don't quote me on this