In 2003, the chief librarian of the city of Santa Cruz, Calif., was able to warn her patrons about whether the FBI had served a National Security Letter (NSL) demanding information about who was reading what books. She managed that task despite specific provisions in the USA Patriot Act at the time that prohibited librarians or booksellers from revealing to anyone that they'd been issued an NSL.
So, how did the librarian get the word out? By regularly reporting to the library board that no NSL had been issued to any of the city's 10 branches, which was perfectly legal. Everyone knew that if the chief librarian failed to report that nothing had happened, then indeed an NSL had been served.
I like it. Better yet, it would be hard to legislate around this workaround…