On our shopping cart we have two options at checkout.
1 ) Registered Customers 2 ) New Customer
Each shows a form to the user. I was just thinking that Returning Customers sounds better than registered customers?
Usually, registered customers are those who you've already got their information (address, payment, login, etc.) on file and/or have created an account, while returning customers are simply people who have visited your site, have a cookie still intact on their system, and/or annonymously purchased from you in the past.
Usually "registered" implies customers are required to log-in at some point, "returning" customers does not.
I like returning customer myself, the fact that they are a customer may imply that they have already undertaken a transaction with you.
I also like the idea of the 'Guest Customer/User' which means they do not need to register in order to use your service. Although you can prompt them to register right at the end if you wish.