Wikipedia, it's a tradition. Even John Paul the Great was buried in red shoes, even thought he didn't usually wear them. I don't see a cross on these, although from what I've read, it's customary.
This pic is from fellow blogger, Rocco Palmo's blog, Whispers in the Loggia. I'm reading his and Father Tim Finigan's blog to see what's happening during the Papal visit to England.
So far, so good.
P.S. Do you think if the Pope clicked his heels three times, he'll be transported to Kansas?