This has been happening at LAX for quite a while now. I have seen it also at the 96th street bridge and the Sepulveda entrances. I have been stopped a few times (I usually drive a SUV) and they wanted to take a look in the back. Seems to happen to trucks and SUVs a lot. I have never been asked to show my DL. At BUR, they have a checkpoint before you can drive into the onsite parking lot and at the valet parking lot, the attendant usually ask to look in the back if you drive a SUV.