My sense is that the USCG has better things to do these days. If boarded, they run a checklist and I doubt the name/hailing port placement is on it. Generally it's just "fix that" -- as in the typical case of expired flares, or no throwable floatation. My personal theory is that we are boarded for crew practice, which I think is a good thing. It is not so easy to board a sailboat in a seaway from a dinghy while armed, and it's an elaborate procedure for a cutter to launch and retrieve crews and coordinate and communicate with radios and laptops. Only practical experience can teach young crewman how to deal with a plunging yacht, get on and off safely, have an effective human exchange with irritated or fearful (or guilty) subjects, and so on. Most boarding crews are in some training stage anyhow. Yeah, I know, this is kinda off-topic--but my videos draw a lot of red-faced outrage over "what right do they have to stop you and search you without persmission!" Well, they do, of course: the USCG is the chief fed law enforcement arm on the water, with full arrest powers. But nobody gets promoted for writing up yacht hailing port placements--Homeland Security is what they are up to, drugs, lone wolves, and terrorists. Especially around here, on the border with Mexico.
My excuse for ignoring the "name and hailing port together" rule for documented* vessels is mere aesthetics. If challenged, I'll change it. But I'm 500 yards from the MDR USCG station, interact with them periodically, and get nothing but good cheer.
There is actually a pretty good reason for yacht name on the transom rather than topsides. A overtaking boat can't hail you by name if they can't see the name.
* Most boats over 35 feet around me are documented. It means not dealing with Cal registration numbers and stickers on the bow, and annual renewal is a single form. The lifeguards, dockmasters and marina managers are alert to expired state regis stickers, as cops are to the sticker on a car license plate.