Beautiful stuff, I sent a few coins.
Why do you want attribution? And how do you want it? "Graphics by BitBoy" at the bottom of every page?
No, you don't have to. I don't know how to go about releasing something under public domain. The above license was taken after the
advice from Theymos. I thought that would be the most appropriate, after all the symbol was traced from the logo done by Satoshi.
Theres a problem with mixing the Ubuntu Font with a derived work from Satoshi and then trying to PD it. IANAL, but they would get very grumpy over it.
Additionally, CC has created CC0 (CC zero) for public domain works beyond UK, US and other countries that dont have a concept of PD.
It would be best to have the BitCoin logo separate from the text, and licenced similarly to licence chosen by Satoshi if it has been traced.
Or you could ask him to declare his work CC0 so you could use it more flexibly.