One day in 1979 I was a service manager at a tiny Honda shop in L.A. when a fella rode up on a CBX. We started talking and it developed that he had just bought the bike and wanted us to check it out. Among other things he wanted to confirm that the bike was in good condition, and to vet the bike in general as the seller had told him it had a new engine.
Many folks are unaware that in the early years Honda actually shipped new engine cases and frames without serial numbers and had their dealers stamp the new parts with an official Honda-supplied stamp set. Before the VIN system was introduced, obviously. However, in all of the Honda shops I worked in, though we had the official Honda stamps, we never used them. We always left everything blank on frame and case replacements. Well, almost always.

So I happened to be eyeballing this customer's bike over closely, and aha! There it was. Blank engine cases alright, with one small difference. That difference was my name engraved on the engine's serial number pad, which I had done to a couple bikes I did crankcase replacements on while I was a mechanic at a shop not very far from this one. So I was able to tell the customer about the bike's recent history. He was thrilled.
1. Due to the bike's propensity for bending its number one connecting rod and holing the cases.