There are many credit card companies that will offer you cash back rewards for credit card purchases that are made using your card. For a lot of those companies, if you use the credit card as a debit card you will miss out on some of those rewards and also have to pay transaction fees. The credit card companies encourage the non-pin transactions because it helps to fight against and prevent fraud. If you are asked to enter a pin number for your purchase, then you can be certain that the purchase is being counted as a debit card transaction instead of a credit card transaction, since credit card transactions do not require pin numbers.
Look at the POS (Point of Sale) machine to see if there is a "Credit" option to pay for your purchase. Most POS machines will have debit and credit buttons. If you can't see the POS machine, ask the sales representative whether or not there is a "Credit Card" option for payment.
Swipe your magnetic stripe that is on the back of your credit card through the POS machine.
Sign the credit card receipt to complete your credit card payment. Be sure to keep the "Customer Copy" of the receipt for your records.
Note that many locations will only require you to sign for your purchase if the purchase amount is more than $25, but as long as you selected the "Credit" option it will still count with your credit card company as a credit card purchase.