The git log should give attribution if needed, and the icons are under the MIT license explicitly (you can find that information in Haiku inc pages about the trademarks and graphics usage).
The MIT license is generic enough that it should work for icons, and if someone has a problem with it, they can always ask the icon author for different permissions.
There is no attribution in the mirror of the icons, and since those arenāt in the haiku tree I canāt assume a license.
@zuMi
You are free to choose what license you want of course, for me personally though it is kind of annoying to have to deal with severall licenses.
It is true that CC was created for such contentā¦ but MIT is fine for it regardless, and matches the Haiku license. 
I assume you ment commercial usage and not non-commercial.
In any case licensing while preventing commercial usage is a bit icky since the MIT license does not match that, and inclusion in Haiku then makes this a bit more difficult.
If I sell DVDs with Haiku preloaded, do i now need to remove those icons? Am I violating the haiku trademark now because I modified the image?
Edit: I do care about this in the context of this rEFInd theme because including rEFind (as a multi-os bootloader) has been proposed severall times, and we could do that, and could (but not have to) use this theme. So making it compatible would be nice. : )
Of course, sorry for the typo.