Why not prick your finger tip, as diabetics do, and leave a fingerprint ?- absolutely foolproof.
Talk about sweating blood for your art!
I guess your fingerprint in your own blood would be convincing. Except that the dried blood would have to be scraped off for analysis, possibly damaging the print in the process.
An inked fingerprint could be faked if the counterfeiters had access to an original work with that print on it.
This is all too James Bond for me. I WISH anyone wanted my stuff that badly!