While debit cards and credit cards are alike in appearance, they differ in one critical aspect: A debit card withdraws money from a bank account, while a credit card creates a loan. Think of them as “pay now” (debit) versus “pay later” (credit). Today’s debit card users often have the choice of authorizing transactions by either PIN or signature. While that choice often makes no differnece to the consumer, it makes a great deal of difference to the merchant and transaction processors. A PIN transaction uses one payment system, the signature uses another, each carrying different fees.