The Mexico City Metro, known locally as the Metro CDMX, opened in 1969 and became one of the busiest subway systems in the world, famous for its rubber-tyred trains and icon for every station. Short recordings of its chimes, brakes and station announcements circulate online as sound effects for videos set in the capital. Creators reuse this clip to instantly signal Mexico City without showing a landmark, and commuters recognise it from daily travel across the network's twelve lines.