Not ALL of them are aware, I'm afraid...
On the Friday afternoon prior to Memorial Day, I was running this Gozzard 44 up the Hudson, on a delivery from Annapolis out to Cleveland...
In Haverstraw Bay, I was flagged down and boarded by watercops from the Marine Division of the Ossining, NY police department... I had apparently attracted their attention due to the lack of registration numbers on the hull, the fact that the boat had the previous owner's homeport of "VAIL, COLORADO" on the transom, and there was an inflatable with very faintly legible Maryland registration numbers hanging from the stern davits...
Clearly, at least from their perspective, I had some 'splainin to do... (grin)
The sole documentation I had aboard were copies of the bill of sale, and a running letter from a documentation service that the application for a new documentation was underway... However, these guys were definitely under the impression that even a documented vessel required a state registration (in this case, Ohio), to be displayed... Took a LONG time, several phone calls to the owner, to get that one sorted out...
It had been years since I was last boarded, and one thing I wasn't aware of... the boarding/safety inspection form I was eventually issued was the same one from Homeland Security that the CG uses - I hadn't realized that local municipalities have apparently been entrusted to perform the same sort of boardings/inspections that the CG has...
Learn something new every day, I suppose... But that one was a surprise, to me...