Tornado warning sirens are a familiar sound across storm-prone parts of the United States, where outdoor sirens alert residents to take shelter during severe weather. Online, that same urgent tone has become shorthand for danger in short videos, memes and edits, even when no real storm is involved. Creators reuse it to set a scene quickly, signal a bad decision or exaggerate a looming problem, because most viewers recognise the sound instantly. Its staying power comes from that instant recognition, which works across languages and needs no context to land.