Only if it is a "check card." Debit cards require a PIN number, but many banks have switched to check cards that can be used as either a debit or credit card. To find out for sure, next time you use your card, hit the "credit button." If it's a check card it will ask you to sign instead of entering your PIN.
The check/debit card must have a Visa, Mastercard or a Discover symbol to work as a Credit purchase but still comes out of your checking account. Discover is just starting up there debit card network.