Capt.Doug writes:

The gear pins mentioned by others here are usually removed by pilots or
mechanics well before pushback for flight. The pin that the pushback crew
holds up is the steering by-pass pin. Without the pin in place, the towbar
is free to swing with the nose wheel steering and could cause serious injury
to persons and equipment. The pin is held up for the pilots to see so that
the pilots know they will have steering before they start taxiing.
Additionally, at my airline and at United, the nosewheel steering is turned
off in the cockpit because the steering may swing momentarily during
electrical power transfer as the engine-driven generators come online.

Thanks for the detailed answer. I was also able to look up "bypass pin" after
reading your reply and got some additional detail ("pin" alone was too
general).

What's the relationship between the tiller and the rudder when it comes to
steering? I understand that most large aircraft have a separate tiller wheel
that can be used to turn the nose gear on the ground, but it also seems that
the rudder turns the gear, too (?), at least during landing and take-off.
What determines the interaction of the two? There doesn't seem to be any
cockpit control that governs how they work in the aircraft I've studied.

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