Doug Podd sensed jeopardy when he boarded a crowded train from the airport to central Paris last year.

A savvy traveler, the Dallas-based commercial photographer secured euros from an ATM in a money belt, and on the train he moved his wallet with credit cards and I.D. to the front pocket of his jeans. He even stuffed a small camera in to make the wallet harder to reach. Nevertheless, when he got off the train, the wallet was gone; the camera remained.

"I...