On ebay there was a claim fro a signed Rubiks cube: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=1714123249
I Contact the Rubik Studio to check if it was authentcic, the answer:
I spoke with Mr. Rubik, who told me the following: He visited Kosalin in Poland once and he really signed a couple Cubes, but on the picture below he is not able to identify his original signature. You can comper this signature which one you can find on your invoice.
This is what i mail the seller:
I did get an answer about your cube see above
So I am sorry but Mr. Rubik can not confirm your signed cube, I have a signed letter by Mr Rubik, this signature has no match with the cube signature. So my conclusion is that you have bad luck and can not sell your cube as authentic since Mr Rubik could not authenticate this signature.