Here in Australia if your boat is registered as an Australian Ship (as opposed to a starte registeration) the port of registry must be
a recognised (registered) port.There is an official list of such ports.
Similar program in Canada except that each boat must have a home city/province corresponding to the owner's province of residence.* It just happens that our home province only has one port of registry, which leads to the bizarre situation of us having the name of a completely landlocked city stencilled on the transom of Gray Hawk.* Coincidentally it also happens that my wife and I both grew up either in or close to that city so its not entirely inappropriate, just weird.