Printer makers did the Secret Service's bidding to fight counterfeiting when they buried hidden codes within color laser printers to show who, where, what, and even when you've made a print. Digital privacy advocates are disturbed that little yellow dots, visible through a magnifying glass, may betray your secrets, as PC World reported last fall. But maybe cops don't need such secret digital codes after all. British scientists have found that no two sheets of paper look alike, as with fingerprints. Within its texture, every sheet of paper bears a unique signature--which neither crumpling, soaking, nor cooking can erase. So if you're a bad guy who's left a clipping of that ransom note at home, burn it.