My Australian model '73 3c had a printed label on the front of the headstock. I don't know what was supposed to be on it because even buying the bike with just over 2,000 miles on it, the wiring loom passing over the label had already wiped most of the print off!
But my UK model Jota only had the frame number stamped down by the swing arm pivot. US Customs didn't have a problem with it, but Florida Department of Transportation were all set to have a major tantrum about no US VIN label. They did accept my explanation that it was a 1978 Italian motorcycle sold in the UK, and that meant it was highly unlikely that a US VIN label would have been installed (not even a requirement here until several years later). But according to a couple of other people here, I was still pretty lucky that I was able to register it at all, many states have a policy of "No VIN label, no number plate. No exceptions."
I don't know how you could import a real vintage vehicle to drive.
Ken