We sign a book in PA, but they don’t have previous signatures in it. I imagine if one wanted to, it would be possible to get the signatures from the driver’s license records for comparison.
Of course, then everyone would need to have a driver’s license or state photo ID, which is the “problem” today.
My daughter says that when she votes in NY that all of her previous signatures are there to compare. The logistics of this method defy my imagination, but it sounds like a good idea.
We have only just started “signing the book” in WI (reform initiated by the Walker adminstration) but there are no comparisons.