I was watching a video and the placard they had was massive! Are they all that big?
I did the USCG documentation for my boat, to get a better interest rate from the lender. I'm glad I did.
There are regs to follow that are not crystal clear.
The "documentation number" has to start "NO." and the letters and numbers need to be 3 inches high. I got my placard from
ComfortHouse.com (went with black letters on white background).
The number has to be "permanently attached" (screws; glue) to the interior structural part of the boat (so it would be apparent if removed). But that does not mean visible without opening a compartment. I have a storage box in the transom that can be lifted out to reach the batteries. There is a nice spot behind that removable box above the batteries where the placard fits well.
You still have to purchase your annual state registration and display your sticker. Since there are no numbers on the hull, I have my stickers low on the side windows. Easily seen from the water, but out of any sight line from the helm.
Finally, there are requirements for the size of the lettering for the boat's name and hailing port on the stern. Mine are in front of and partially blocked by twin outboards, but still visible from the right angles.
Police boats have passed me many times without incident. I even pulled up for gas next two two police boats. They can see the current registration stickers, and the boat's name and hailing port on the stern, and they either assume its documented or can look it up. Have never been questioned.