The requirement is also for 3" letters, minimum. It used to be the case that the "hailing port" could be the city and state of the CG documentation office where your boat became documented. It could also be the city and state of where your boat was berthed, or the city and state you lived in. Since one cannot put "St. Petersburg, FL" on the transom of a Pearson 30 in 3" letters along with the name of the boat,

we used Miami, FL as the hailing port b/c that's where the documentation was processed. Now, however, all of the documentation is processed out of West Virginia; so I don't know if that prior option still exists. On the Bavaria, the transom is wide enough for "Long Beach, CA."
FYI-the good thing about CG documentation is that it's a one-time charge, with no annual renewal fees as with some State registrations, and no State registration of your dinghy, even with an engine, is required if it is used only as a tender to the documented vessel. In CA the DMV people will try to tell you that that is not true; but it is. You just have to "splain it" to 'em.