Err... if you're asking for legal purposes, I'm not qualified to answer that. I believe that when licensing something as CC-By, the author can specify a name/handle and optionally a url that needs to be put there, but most of the time they don't actually specify one so it ends up falling to the discretion of the person reusing it. When reusing a CC-By asset, I think it's pretty standard practice to list the author's name/handle and where you got it or what project it's from. Of course, that is harder for some projects than others. For example, Dark Magic was a collaboration between a lot of us. I think in those cases it's standard to credit the development team. For instance, if you used assets from 0 A.D., you would probably just credit Wildfire Games.