A metro: frequent underground train found in built-up areas with high populations. Generally depicted as a forward-facing train traveling along tracks or rails and emerging from a tunnel. Color varies by platform, but most designs feature red-accented trains.

Apple's artwork shows the characters IL2 which may refer to one of the more locked-down buildings at Apple's Infinite Loop Headquarters during iPhone development (IL2 = Infinite Loop 2). WhatsApp includes an “M” transit-style logo, like the Ⓜ️ Circled M emoji, as well as an “F” route marker. JoyPixels displays “JOY” above the windshield.