Use ATM PIN if you are using your Debit Card for Retail Shopping - RBI Guidelines
As per RBI (Reserve Bank of India) guide lines from 1st December 2013 onwards, those who wants to shop with their Debit cards need to key the Debit Card PIN number. If you provide the Debit Card, then shop keeper will be asking to key your debit card pin number in to the machine. Then only the transaction will happen and slip get generated from the machine.
This is to secure the Customers, other wise if some one loose thier Debit card, by the time they will know that their card got missing some where, if some one uses that card for a retail transactions, there is no other way to get the money back from the Bank as like Credit card. Hence RBI made this as mandatory for all those who want to use their Debit cards for shopping.