'Dark Knight' ad push is an event in itself

The billboards arrived without fanfare or explanation in more than a dozen major cities last May. Bearing two simple catchphrases, "Harvey Dent for district attorney" and "I believe in Harvey Dent," they featured a photo of a stately Dent (imagine Eliot Spitzer with a shock of blond hair) against an American flag.

But within 72 hours, each billboard had been defaced by identical graffiti: The candidate's eyes were scrawled over with black rings, his lips crudely rouged with a smeary, clownlike grin. As well, each of the placards' messages had been altered to read: "I believe in Harvey Dent TOO."

Although not outwardly advertising anything other than Dent's political aspirations (never mind the impossibility of running for D.A. in more than one city), the billboards were the opening salvo of one of the most interactive movie-marketing campaigns ever hatched by Hollywood: a multiplatform, hidden-in-plain-sight promotional blitz for the new Batman movie, The Dark Knight, which stars Christian Bale and Heath Ledger and reaches theaters July 18.

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