Originally Posted by TWA884

There is a TSA security checkpoint at the exit from the bag drop off area; just follow the signs for transfers or connecting passengers. That checkpoint is considerably less busy that than the others.

Here are photos from a post by Microwave in the LAX AA T-4 - TBIT secure airside connector (open Feb 2016) in the American Airlines forum from 2016 showing the way to the TSA security checkpoint as you turn right when you exit the baggage drop-off area. If you go straight ahead, you'll end up on the sidewalk outside the building.