To guard against identity theft, John and Mary Benbow of La Jolla took their first names off their personal checks, using their initials instead. They shred documents that show any of their identification numbers and carry credit cards only when they plan to use them. Whenever they see a doctor or go to the pharmacy, however, they must present Medicare cards inscribed with their Social Security numbers — numbers widely viewed as the keys to identify theft. Photocopies of the cards are routinely attached to their medical records, making the information available to anyone with access to their files. Seeking...