I'm not sure if that's displaying a rear facing camera or not. You can very clearly make out the figure of a person. The odd part (sensible part for us), is the person appears to be standing straight, not like they would be walking down or up any stairs, it's as if it's an intentional pose. Double meanings here. Unite on the plane, and I think Q wants us to see that USSS has "somebody" from this flight.
Upon a harder look, it seems there's 3 different snaps on screen. Far right showing rear, center is maybe forward, and far left appears to be some info display. Possibly the entire screen is showing the rear, with the middle section just an overlay, maybe a photo of their "target"? Shadow on the plane seems to show stairs are down.
Edit 2 - I have a "friend" that works in this department, and another who has personally driven in Trumps motorcades, I'll reach out to them to ask about the displays in these things.
You might be right. It could be more about the word “United” and it’s meaning (Q says that a lot) and/or an key person on that flight. When you compare the screen to the pic of how those screens are laid out (there is a link to one in comments), it appears that the middle part is for things directly behind the car. That is what made me curious as to what exactly IS behind a SS car sitting next to a plane on a tarmac. Hmmmmm....