So, the other day, SayUncle reported that he had been watching Firefly on DVD, and found it Gorram annoying that the profanity was rutting contrived. "Cuss like you mean it!", he said.
He was immediately inundated with comments--well, it would be an inundation here, over there it would be a light day--explaining that it was done to include Science Fictiony swearing while avoiding the censors, because, after all, it's the future, and a sort of American-Chinese hybrid future in a different star system, so what did he expect?
I think they might have emphasized the future/science fiction part more. In an essay on writing SF--it could have been from his James Forrestal speech at Annapolis--Robert A Heinlein (pbuh) said that he recommended establishing right away that one's story is not set the current day; he said that his favorite was the phrase "The door irised open." Certainly, the Heinlein "juveniles" that opened with the teenaged son driving the family helicopter home made it pretty obvious, too.
Different authors handle it in different ways. In his Known Space series, Larry Niven has one planetary culture adopt the fashion of the Assymetric Beard: Half a sideburn, half a mustache, partial goatees, etc.* Meanwhile, on Earth,pills were taken to change one's skin and hair color, and even to apply patterns to the skin, as sort of temporary, painless, whole-body tattoos.
It's not always necessary to make the differentiation, of course; if the story opens with soldiers in powered armor, , or someone using a teleportation booth or flying with a jetpack, let alone on a starship, it's pretty obvious.
However, if the story line can be described as "Space cowboys", then Measures Must Be Taken...
*I had already been thinking about this when I saw Uncle's post, because I had managed to miss about a two-inch long, eight-of-an-inch wide section of beard when shaving before work the day before. Not visible in the mirror, but obvious to the touch...