Quote:
a nose lock was used on push-back and SOP was to show it to the crew once the tow bar was removed. The pin that is shown to the flight crew is the steering lockout pin (also known as the Hydraulic Bypass Pin). If this had not been removed then the aircraft would not have made it to the runway (unless it was a straight line to the runway). The U/C lock pin is a different pin and is located higher up in the wheel well.
Not always:
ATR42/72 Aircraft, some airlines use a pin for Pushback but its not a steering lock out pin. Its a nose gear pin. The reasoning I believe is to prevent nose gear collapsing due to excessive pushback & towing.
Also the Ground handler has a responsibility, as they are usually responsible for the pre-departure walkround in which Gear Pin checks are part of.