I put flyers on my wall of every machine I own, or have owned, as a kind of museum. I only have those flyers signed. I never have the pins signed. So, I had Dirty Donny sign my MET flyer, for example. If/when my Met leaves my collection, that flyer with Donny's signature will still be here for me to enjoy.
I'd probably consider a celebrity's signature on a flyer of their relevant pin, for my own enjoyment, but wouldn't have the pin signed in hopes that the value was raised.