[drc]

Obviously, it's nice to have the photos of Ali signing. Without those a lot people would be that much more suspicious.

What would be great too would be some sort of paper documentation or other evidence that Ali was hired to sign these, or at least sign for your dad/grandfather. I assume there was an agreement/contract, payment check.

Documentation/evidence your dad/grandfather had Ali do a signing + your photos of Ali Signing posters with the same design = good for cause. If you had a copy of the actual contract for the signing, that would be hard to beat.