In Florida when I first got my TI in early 2010 I was pulled over by the shore patrol, I tried to outrun them but they had a 35 ft Scarab that will probably do 70+. They told me since the boat was longer than 16 ft it probably should be registered, they didn't give me a ticket or anything, but I imagine if they came across me a couple weeks later, I would probably get a citation so I went ahead and registered the boat. What an affair that was, it took about 2 months of going to the DMV, then going back to the dealer many times trying to get the certificate of origin (nobody had ever registered a kayak before so nobody knew what to do). The people at the DMV office finally had to call down state for instructions (quite a cluster).
Actually that was on my second time out on the boat, on our first outing my wife and I got stuck just outside big pass while the tide was running out (about 5 mph current) near sunset when the wind died. We are both really experienced Hobie kayakers and are used to pedaling up to ten hrs, then get up and do it again the next day, but that day got the best of both of us, so I was given a free ticket (from wife) to purchase an emergency motor for the boat anyway and we all know anything with a motor (gas or electric trolling) has to be registered regardless what it is, so it was a no brainer getting a title and registration anyway. Since then I have never been out without my emergency motor mounted to the boat, so it has to be registered anyway. Also my insurance agent suggested we get the boat registered and titled (much easier to track down if stolen).
There is plenty of room to mount the numbers to the bow on either the AI or TI, here is a pic of my numbers after a couple years on the boat (if anyone finds my letter L out floating on the water please return it to me LOL).
This is my 3rd TI now and I usually don't do anything to replace missing numbers until I'm down to the last couple. as long as the orange or red sticker with the actual registration on there they don't seem to bother you if a few numbers are missing here and there.
To get the numbers to stick on the PE hull is another matter. What I do is rub the hull down in the area I want to place the letters with rubber cement thinner (Bestest thinner available in the paint department at Home Depot), any brand will work as long as the active ingredient is Heptane (heptane is the aromatic in gasoline that makes it unstable so be careful), the longer it soaks on there the better it works. Heptane melts and softens PE plastic and helps you prepare the surface for painting. I then spray a coat of Krylon clear coat (for plastic) over the area where the numbers will be placed, the active ingredient in the Krylon paint for plastics to make it stick to plastic is Heptane. Once the paint sets up a little you then place the numbers onto the boat (the adhesive sticks to the paint much better than the PE). After the numbers are placed, I spray a heavy clear coat over the top of the numbers so it pools around the edges of each letter (this is actually what holds the letters down). Once done you should get years of service from the letters.
Here is a pic of my lettering on the AMA that's been on there a at least a year or two now.
On one of my hulls I used stencils and spray painted the numbers on, what a pain that was, using adhesive boat numbers is much simpler.
Without any surface prep the letters last about a week or two, then start peeling off ( I'm just sayin)
Hope this helps