In 1988 the rise of expertly managed consumerism became a topic of heated debate. In the movie They Live this heavy handed theme is presented in a science fiction format. Rather it is the other, alien, perhaps ancient humanoids that have taken power in the aggressive yet peaceful means. Instead of an us versus them mentality of the invaders from beyond, certain humans have allied with the others.
Here is the hero, played by Roddy Piper, of the story with gun blazing. He is doing a Reverse Terminator as the hero unleashes violence on the 'other' rather than have people suffer from the machine mind.
The US flag was placed as the background purposefully as a statement. Its message can all depends on the observer, but one can assume this movie is making a statement about taking a stand against a corrupt system.
It looks like the flag of Peru makes a small appearance in this movie. You can just barely see flag above the cashier's head. It looks like the flag of Canada, but remember it was designed long before the Canadian flag.