Recently, many folks in the San Francisco Bay Area and other areas have reported receiving supposed parking tickets that were issued by the private company that owns the land on which their vehicles were parked. While it's okay for private entities to contract with cities to process traffic citations issued by cities by their own city employees, it is not legal for private companies to issue parking tickets for supposed violations that occur on private property. According to a December 23, 2011 formal opinion of the California Attorney General, neither Vehicle Code section 22658, nor any other state law, allows for this. While vehicles parked on private property may lawfully be towed where parking is unauthorized or in violation of stated time or other restrictions, and the appropriate sign warning of the possibility of being towed has been erected, the law does not authorize the issuance of parking tickets by private entities that require the payment of parking penalties.
If you receive what looks like a parking ticket while parked on private property, such as a shopping center or business park, look at it closely to see if it was issued by the city (or, in unincorporated areas, the county). Keep in mind, though, that parking tickets issued by cities for violations on public streets often refer to private companies that legitimately contract with cities to process those tickets. But if the ticket shows no indication that it was issued by a city or other public entity, you can safely disregard it.