POZZUOLI, Italy — The sailor parked his car for just 15 minutes. Petty Officer 3rd Class Thomas Dickenson left it along a busy row of shops, restaurants and bars where he met up with some friends. But when he returned, his rented subcompact had vanished. "I’ve been told by Italians, ‘Oh my gosh, I can’t believe you parked down there,’" Dickenson says. "I had theft insurance, thank God." The sailor is just one casualty in a plague devastating the Neapolitan suburbia. The buzzing hubbub of Pozzuoli makes it painfully apparent that people have the cars to swipe. As many as...