Searching for a quick, effective way to evoke the warlust-driven future world of Starship Troopers, director Paul Verhoven created a series of fake TV spots that characters watch in the movie. You can see one this clip, a patriotic ad for the Mobile Infantry which captures both the weirdness of a future where humans fight bugs, and the familiarity of a culture where TV commercials are still bizarrely perky and strained. Other scifi creators have also gone the Verhoven route, adding realism to their alternate realities by peppering them with ads. See some of the creepiest and best of the bunch below.
One of the most infamous fake commercials from a scifi movie is this ad for Fruity Oaty Bars, a made-up product that appears in Firefly spinoff flick Serenity. Director Joss Whedon wanted to evoke the Asian-Western mashup culture of the far future in this ad, which looks like a mixture of Indian, Chinese, Japanese, and North American iconography. In the film, it also contains a subliminal message that sets off government experiment River's "kill kill kill" programming — when this perky clip airs in a bar, she goes apeshit and murders everyone in the joint.
Another popular scifi ad is this one, for the soft drink Slurm that Fry loves so much in Futurama. It's pretty much a pitch-perfect parody of typical soft drink and beer ads, with the single futuristic addition that the company admits that the drink is literally addictive. Oh, and it's being sold by a mutant snail.