I think Vapor said it- the PYOs were made for us to paint and I think that whomever paints one should sign the felt bottom. Like Arlla said, Windstone gets its credit from the felt logo and the sculpt Pena stamp…not to mention its unmistakable and highly detailed statue to begin with.
Personally, any PYO I would get from someone, I would at least want them to sign and date it. Putting anything more is solely up to them. That way, should I ever actually get more than one or 2 pyos painted by forum members, I can know who did what since my memory isnt what it use to be.