A lot depends on the nature of this private street. If it is accessable to the general public (i.e. it is not a gated community) it is possible that either the parking officer improperly cited you because they believed your community was city property, or, there was/is an agreement with the developer/HOA that the city will enforce all the ruiles of the road within the community. If the community's roads are not discernible from the rest of the city, it could be an accidental issuance.
If the police are permitted or requested to enforce ANY vehicle code violations within your community, they are likely permitted to enforce them all. But, if you do not want them dealing with speeders, reckless drivers, etc., then they can certainly leave everyone to their own devices.
And specifically, CVC 5200(a) states: When two license plates are issued by the department for use upon a vehicle, they shall be attached to the vehicle for which they were issued, one in the front and the other in the rear.
The section does not seem to indicate whether "private property" is an issue or not ... though I would think that it would have to at least observed in a place where the officer had a lawful right to be. So it might be a sticky wicket.
And we CAN stop you solely for not having that front plate missing or improperly displayed. And CA always issues two plates.
Ultimately, you may have to do some research as to the arrangement with the city. My guess is that unless the community is gated or is obviously a private community (like an apartment complex or mobile home park) the police are entitled to enforce the vehicle code within your community. And if it is obviously set aside from the public throughfares, my guess would be that the citation was isued in error.
- Carl