Are these "Signature" and "World" products really premium cards, or just another marketing ploy, like a "Titanium" card I've seen floating around out there?
World MasterCard is a MasterCard product, and has specific meaning, as does Gold and Platinum. This is unlike Titanium or some of the other more creative names out there that individual banks have created to sound impressive without necessarily providing any benefits. I believe that Signature Visa is also an official product.