Cassandra Gambit

An organization, often a Government Agency of Fiction, deliberately releases secret information, sometimes within a work of fiction, in order to invoke a Cassandra Truth. Alternatively, an individual or small group may do this to get the word out to allies and others in the know despite people/groups/governments who don't want the word to get out; the fictional/tabloid nature of the outlet provides cover for these Cassandras to stave off retaliation from their opponents. They're just Genre Savvy enough to know that You Wouldn't Believe Me If I Told You. It also allows them to honestly state, "Well a lot of people got that idea from this book, which is a work of fiction". They can then turn on their critics and say they're too credulous or are confusing fiction and reality.

The differences between this and Sarcastic Confession are that the confessors aren't being sarcastic, and they are addressing themselves to many people rather than one or two. Unlike a Public Secret Message, which is published in the open but in code, a Cassandra Gambit is straightforward: what is said is what is meant. She knows others won't believe it, but hopes someone out there ("the right listener") will believe and act on it.

Compare Getting Crap Past the Radar, Hidden in Plain Sight, and Refuge in Audacity. The topic these Cassandras are warning about is likely to be the Elephant in the Living Room.

Anime and Manga

 * Haruhi Suzumiya - Invoked by Kyon when he tells Haruhi the truth about the members of the SOS Brigade: that one is an alien, the other an esper  , and the last is a time traveler  . Haruhi appears to buy this and even correctly guesses each of their indentities... right before blowing up at Kyon for thinking she'd be dumb enough to buy any of it!

Film:

 * Played for Laughs in Men in Black: you know all those tabloid stories that are obviously just made up? Yeah...
 * In Deep Cover, Laurence Fishburne has to Take a Third Option when asked by a gang of thugs if he's an undercover cop. If he lies, then any future arrest would be worthless because it'd be considered "entrapment". And of course, if he tells the truth, they'll kill him. So he just tells them the truth in a way that makes it seems ridiculous. (Note: This is actually a case of Artistic License Law. Real cops don't have to tell their marks that they're undercover. The entrapment clause doesn't work that way. Because if it did, there'd be a lot fewer arrests and a lot more dead cops.)

Literature

 * In play for a time in the Harry Potter universe, when The Quibbler (regarded as an unreliable tabloid) is used to get the word out about Voldemort when The Daily Prophet adheres to the Ministry of Magic's official line (that Voldemort is long gone/dead).
 * The alchemist gives this advice to the protagonist in The Alchemist, a book by Paul Coelho.

Live Action TV:

 * In Stargate SG-1, Wormhole X-Treme!, a Show Within a Show that parodies the main show, is allowed and even encouraged by Stargate Command, because, well, this.
 * Seven Days: a Conspiracy Theorist gets Frank to go on TV, and Frank tells the world about the Project. Nobody believes him.

Web Comics

 * The Comet in Scandal Sheet exists for this.

Western Animation:

 * Area 51 in Kim Possible plays this trope to a T, so much so that Kim and Ron are surprised to find out that Area 51 is exactly what the tabloids claim it to be.
 * On Futurama, when Area 51 recovers a crashed "spaceship" (Bender) and alien "invader" (Zoidberg) in 1949, they invite a conspiracy theorist to tour the facility specifically because no one will believe him.

Conspiracy Theories:

 * The F-19. The Air Force said that the F-19 didn't exist, encouraging people to speculate that it did, leading some to speculate that this was done deliberately to create a decoy project to protect the F-117.