I have no idea how many were hand signed by the assembly person.
But they were early models.
A several years ago, I was having coffee with a fellow RC51 owner who bought his new back in 2000.
He was out riding with his buddies when his engine seized up solid.
He complained to the local Honda shop he bought he bought it from and they were giving him the run around.
So he took it up the food chain to Honda Corp., and when they found out what serial number it was, they replaced his entire bike (which went back to Japan).
Honda replaced his with a brand new bike and even swapped all his aftermarket goodies over to the new bike.
I'm thinking assembler 'X' had to explain his handywork and why his engine seized.
This owner is the one who told be about the hand signed engines.