Mind the gap has been the signature safety phrase of the London Underground since the late 1960s, when automated announcements and platform markings were introduced to warn about curved platforms where trains do not sit flush. The wording became so familiar to commuters and tourists that it moved onto souvenirs, parodies and travel videos, and later into online edits as a shorthand for any risky step. Its polite, unmistakably British delivery keeps it instantly recognisable far beyond London.