Your hailing port should be where the boat is docked, but where you live is also common.
Click here to see the CFR regs:
http://tinyurl.com/3gkks8
Legally, the regs say this:
A Hailing Port is your choice of city to be marked on the vessel. You can choose any city in the United States as prescribed in the U.S. Dept. of Commerce's Federal Information Processing Standards Publication 55DC. You must display it on the outside of your vessel in compliance with prescribed instructions.
Also, regarding size of lettering:
Official Number and Hailing Port Regulations
On ALL vessels the OFFICIAL NUMBER must be permanently marked in block-type Arabic numerals not less than three (3) inches in height on some clearly visible interior part of the hull and that the number cannot be obliterated or obscured.
On vessels exclusively designated for PLEASURE the name and hailing port should be marked together in clearly legible and durable letters not less than four (4) inches in height on a clearly visible exterior part of the hull.
On COMMERCIAL vessels the bow and stern markings must meet the following requirements:
BOW MARKINGS:
1) marked in clearly legible and durable letters not less than four (4) inches in height on some clearly visible exterior part of its port and starboard bows.
OR
2) marked in clearly legible and durable letters not less than four (4) inches in height on clearly visible exterior parts adjacent to the port and starboard bows in order to avoid obliteration.
STERN MARKINGS:
1) marked in clearly legible and durable letters not less than four (4) inches in height on some clearly visible exterior part of its stern.
OR
2) marked in clearly legible and durable letter not less than four (4) inches in height on a clearly visible part adjacent to the stern in order to avoid obliteration.
