Steering column lock
Engaging
When the key is to STOP or PARK remove the key and turn the steering wheel until it locks.
Disengaging
Rock the steering wheel slightly as you turn the ignition key to MAR.

WARNING
Never remove the ignition key while the car is moving. The steering wheel would automatically lock as soon as you try to turn it. This also applies when the car is being towed.
WARNING
It is absolutely forbidden to carry out whatever after-market operation involving steering system or steering column modifications (e.g.: installation of anti-theft device) that could badly affect performance and safety, cause the lapse of warranty and also result in non-compliance of the car with homologation requirements.
Test yourself
A quick Fiat Punto quiz: every answer comes with an explanation and a link to the manual page.