HaveIBeenFlocked.com compiles Flock audit logs, allowing users to type in their license plate number, and the website returns information on search results, including whether or not a Flock system operator has searched the database for their license plate.
The audit log includes the stated reason that someone in law enforcement gave in order to look up the license plate, but doesn’t include if or when your vehicle passed one of the Flock cameras.
Start with “NOPLATE”, “NCC1701”, “XXX” and “NULL”.
There might be others that have ended up in the news as a result of human (police or programmer) error, but just those four over fifty States is a good 200 to start with.
Go drive/walk by your local police station and note all the plates of unmarked cars in the area. Many of them are likely police vehicles or private vehicles of employees. Do the same near a courthouse. Use those as fodder for this tool.
For Virginia (Number)-(3 digit number)L are local government vehicles and (number)-(3 digit number)S are state government vehicles. State police and those belonging to members of the General Assembly just have incrementing numbers.