The whistle comes from The Flintstones, the Hanna-Barbera animated sitcom that premiered in 1960 and set modern family life in the Stone Age. Fred Flintstone works at a rock quarry, and the end of his shift is signaled by a bird-powered factory whistle, a visual gag built around prehistoric versions of modern machines. Clips of that moment were later ripped from cartoon reruns and shared on soundboards and in edits, where the blast became shorthand for finishing work, escaping a boring task, or making a dramatic departure.