Hmm. I do recall Nike taking out some design patents on the BTTFII shoes.
Design patent 329,126.
You'd have to check the US Patent & Trademark Office. They have a search engine that can help, but the terms are probably going to be very generic. The Nike one says 'The ornamental design for an element of [shoe] upper.'
Your best bet would be to search for the names of the prominent artists.
-Mike