Romulans are a major alien faction in Star Trek, first seen in the 1966 Original Series episode Balance of Terror, and closely associated with cloaking technology that lets their warbirds vanish. That stealth identity has carried through later series and films, making cloak sounds a shorthand for Romulan ships online. Fans cut the short effect for edits, games and memes, and it stays popular because a brief shimmer instantly signals an alien ship disappearing, even for viewers who only know the franchise casually.