It sounds like something out of a summer caper flick: Two men carrying Japanese passports were apprehended trying to enter Switzerland from Italy via commuter rail in June. The men looked out of place on the train, which tends to carry low-income manual laborers. That was enough to raise the suspicions of the Italian authorities, who detained the passengers and rifled through one of their briefcases. Inside was what appeared to be $134 billion in U.S. Treasury bonds labeled with denominations of $500 million and $1 billion. (This despite the fact that the Treasury has never produced bonds in denominations greater than $100,000.)  Later this summer, history seemed to repeat itself when Italian authorities intercepted another cache of false T-bills from the...