The code enforcement officer is responsible for maintaining the quality of life in a community. The fact of the matter is disorder and crime are usually inextricably linked. According to the broken windows theory, if a window in a building is broken, and is left unrepaired, all the rest of the windows will soon be broken. This is as true in upper income neighborhoods as it is in lower income neighborhoods, and the same theory applies to vehicles that are considered junk or inoperable.
In many residential communities, it is considered a nuisance and unlawful for any property owner to have a junk or inoperable vehicle located on their property. For clarification purposes, a vehicle is traditionally defined as an automobile, truck, motorcycle, motorbike, boat, trailer, or camper. Bottom line is this, if a vehicle cannot be lawfully operated on a public street due to circumstances such as lack of current and valid state license or registration; nonexistent, insufficient or inadequate safety or other equipment required by law for legal operation, then that vehicle should be considered junk or inoperable by a code enforcement officer and qualifies as a violation. A car cover does not make the violation go away!
If you observe a vehicle that cannot be mechanically operated due to circumstances such as an inability to start and/or operate as designed and intended due to a mechanical or physical defect or damage; deflated tires; broken or inoperable turn signals; or broken or inoperable headlights; then that vehicle should be considered junk or inoperable by a code enforcement officer.
If this specific language is not in your code of ordinances, then you as the advocate of codes in your community should work towards amending your ordinance. Your role is to visit the location, conduct an inspection, and provide direction on how residents can come into compliance with the regulations. Enforcement is a tool and compliance is the goal!