What violation occurs when a vehicle is parked without locking the doors and the key left in the ignition?

The violation of failure to secure a vehicle is identified when a vehicle is parked without locking the doors and has the key left in the ignition. This situation poses significant security risks, as it makes the vehicle susceptible to theft or unauthorized use. Properly securing a vehicle entails not only locking the doors but also ensuring that no keys are left inside, as this would enable anyone to easily access and potentially steal the vehicle.

The other choices address different scenarios: an illegally parked vehicle pertains to violations of parking regulations or restrictions, failure to display a valid license is related to operating a vehicle without proper licensing, and unauthorized vehicle repair deals with maintenance or modifications being performed without permission in restricted areas. However, none of these are relevant to the issue of a vehicle being left unsecured.