I saw the same sort of thing happen to my father once in a store. Unfortunately, his voice is also affected, so it was really hard for the clerk to understand him. I didn't get there until just after this happened, or I would have given her what for! Dad's hand stops moving to the right, while his fingers continue to write the letters. This results in overlapped letters. This past Christmas, I was able to locate a paper that he'd signed before the PD onset, and I had a rubber stamp made for him. Unfortunately, I didn't realize that he sometimes signs his name "Gerald" and not "Jerry" as on the stamp. So now I'm looking for something he signed pre-PD with "Gerald" on it! Oh well, guess I solved part of the problem.