So, I think I figured out what “these people are stupid” marker stands for.

Beavis and Butthead, season 2 episode 10. It’s called “way down Mexico way”. It’s a direct quote from the show.

Beavis: M-80s?

Butt-head: Firecrackers?

[Mexican woman shrugs]

Beavis: Fireworks?

[Mexican woman shrugs]

Butt-head: These people are stupid.

So my conjecture is that every time the cabal attempts to sneak something across the border, Q uses that marker.