[RickT]

Lots of Documentation Companies will document the boat for you but few will provide a sign board or instructions on permanently affixing this number to the hull. The cheap way to do this is go to your marine supply store and buy the Black stick on numbers you can use for applying the state registration numbers to your external hull. Then apply them to a stringer or some location that is visible in the engine room. To make them permenant, put a coat of West System Epoxy over them.
The Proper way to Show these is

"NO.1234567"

The NO. belongs there followed by your official number. The Coast Guard calls this the "Official Number" . The documentation number never changes as it goes from owner to owner. It stay's with the boat for life.
It is possible and probable the boat has been documented and the number was never put on the boat.