I have used Visa exclusively for 15, now I have my first Discover card.
A notable difference is that Visa always carries the name of the bank (for me it was Chase); but the Discover card does not. This made the distinction clear -- Visa provided clearing services and Chase is the one that I owed money to. Also, it was Chase's (or my "Chase Amazon.com") phone number on the back.
Who is the bank that is giving me credit with my new Discover card?