Word of caution!
If you go up to the parking garage across from Terminal 3 and the Tom Bradley International Terminal (or any parking garage for that matter), you will most likely be questioned and/or asked to leave. Or even possibly detained if you are not careful! Anywhere on the airport property where you are loitering (including spotting and such), you will get the attention of security-minded travellers and airline/airport staff as well as TSA
, airport security and airport police.
Your best bet is if you are within a secured area, such as inside the concourse and/or Terminal building, you will be left alone to spot to your heart's content!
It sucks, but this is the post 9-11 world we live in!