Which groundbreaking marketing campaign involved placing mysterious symbols in newspaper ads and creating online puzzles that readers had to solve before the book's release?

The publishing industry has seen some remarkable marketing campaigns that transformed books into cultural phenomena. Beyond great writing, strategic promotion has launched many literary works to unprecedented success. This trivia tests your knowledge of innovative book marketing campaigns that changed the publishing landscape and created literary sensations. Do you know which unconventional promotional strategy catapulted an unknown title to bestseller status?

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The Da Vinci Code's 'Crack the Code' campaign by Dan Brown, which included cryptex puzzles and a $10,000 prize for solving embedded clues
Harry Potter's 'Platform 9¾' campaign, where fake brick walls were installed in major train stations for fans to 'pass through'
The Hunger Games' 'District Identity' campaign, where fans could register as citizens of different districts and receive specialized content
Gone Girl's 'Missing Amy' campaign, featuring missing person flyers in major cities and false news reports about a disappeared woman