I received a corp. credit card in the mail where the envelope looked as though it had been run through an old-school credit card carbon copy machine to get the imprint of the number. I called up the issuer who bounced me to the internal security team -- it took them quite a while to understand what the problem was but they were happy to send a new card. Never found out if it was an intentional attempt to steal the number or an artifact of a sorting machine but there did appear to be purple ink on the outside of the envelope.