The issue number of a Barclays debit card can't be found on the card. Issue numbers are typically located on the front of the card, and normally it is indicated as ‘01′ unless you have had your card replaced at any time.
If you check the card face of the Barclays debit card, what you see is just the 16-digit number which represents the card issuer and your specific account number. On the back side of the card is the CVV2 number, or security code number. The last three digit number on the signature strip is used by merchants as a way to verify that the cardholder is present at the purchase.
According to sources, Visa's tend not to have an issue number; they're typically reserved for Switch Maestro and Visa Electron.