In Florida if you have a motor (even a trolling motor) the boat must be registered and have the numbers displayed on the bow.
Once you know what to do it is very simple and quick, but doing it wrong or without the correct information can be very frustrating. The first kayak I tried to register took me three months of frustrating emails, doing to the DMV repeatedly, on and on... Once I figured it out I know what to ask for now from the dealer when I buy the kayak, and I go straight to DMV and register everything right away, if you have all the right stuff it just takes ten minutes and only costs a few bucks. It's worth it if not for anything else insurance reasons, for if it is registered and it gets found you will be notified, if never found you can file insurance claims, etc. So it is definitely worth registering you kayak (especially a very expensive one like a Hobie).
First of before contacting anyone else (ie like DMV, etc) get the hull number from the back of your boat (It is engraved into the hull on the right rear of the hull, it is usually on the sales receipt as well).
Then contact the dealer who originally sold the boat to it's first buyer (if that's you is easier). The Hobie dealer who sold the boat originally is the only one who can give you the manufacturers statement of origin ( called the MSO document). This document was sent by Hobie to the dealer along with the boat, and you need to have that specific document and can only get it from the dealer (Hobie company cannot provide that document for legal reasons). It is also very important to have a copy of the original bill of sale. If you purchased it used from a third part, you need to get a bill of sale from them, basically this sale document proves that sales tax was paid for the boat originally, if you can't produce the receipt Florida charges you full sales tax on the price you paid for the boat.
Once you have the certificate of origin (the dealer knows exactly what it is), and a copy of the sales receipt you are now ready to go to the DMV.
First thing they will do is create a title for the boat (about $10 bucks I think, this is a one time charge). Once titled you then get a registration tag, and you attach it to the bow of your boat along with the registration numbers (everything is explained well in the documentation).
Go to this thread to read up more on MSO viewtopic.php?f=18&t=48596
Hope this helps