I've just read the excuses!
I'm stunned that someone can just turn up and drive, no control, no briefing, no sighting laps, probably no idea what the circuit is, or that there will be trucks merging... nothing. It's dangerous as well as selfish/stupid.
I agree with you Hoyin and Andy - there needs to be stickers on the windscreens. That's extremely cheap to organise, and of course would only be distributed to the team leads at the morning briefing. The more I think about it, the more astonished I am that it hasn't been done before. Cars without stickers can easily be seen and held at the pit exit, just as they hold cars for the trucks.