[Ysharros]

As far as I know if you *don't* pick one at creation you don't currently get the option to pick one later. That may not always be the case, since many people have been burned by this - given that many other games make you wait to choose a surname, a lot of people assume they'll be given the chance if they don't do it at creation.

I expect we'll see options to add or change a surname, but I don't think they're available now. So if you want one, make sure you give yourself one when you're creating the char.