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.