When we lived in Virginia, even though the mothership was a federally documented vessel, the dink (when used with a motor) had to be registered in the state (note that most other states you will travel to, will require it to be registered in SOME state to be
legal for use in their waters - at least for some grace period before they'll want your
money to register it).
Once you register the dinghy the state will send you a
registration number and 2 yearly (or multi-yearly) stickers. You then must apply the numbers and stickers to the dinghy, either by painting the numbers on the
hull (difficult) or adhering rubber numbers to each side (expensive at ~$2/number); some folks put the yearly sticker and numbers on a plastic number plate (available at West Marine) that is hung along each side whenever they intend to use the dinghy. We just sewed the numbers and sticker (sandwiched between clear vinyl) onto our dinghy chaps. You should also carry a copy of the
registration in the dinghy - you may be asked for that paperwork if pulled over by the
water cops.
Then you may get a tax bill from your county for yearly personal property tax on your new dink and
motor, if the county where the dink resides assesses this tax. If you are not in the country on January 1 of the tax year you do not owe tax (i.e., you took it to the
Bahamas or Florida), but you'll need to inform the county assessor of this fact.
Sure you don't want to just row your dinghy?