If you're new to kayaking, you might be wondering if you need to register your kayak. The answer is maybe. In the United States, boats 16 feet and longer or any vessel with an engine must be registered with the state in which it will be used most often. This includes canoes and kayaks propelled by motors or sails. Some states have additional requirements, so it's best to check with your local Department of Natural Resources or Fish and Wildlife agency. If you're only going to use your kayak on private property, like a lake on your friend's property, then you don't need to register it.
Most states require that all watercraft display valid registration numbers on both sides of the bow (the front of the boat). The letters and numbers must be at least 3 inches high and in block characters that contrast with their background color. You'll also need to display your validation decal next to the registration number on each side of the bow. Some states require that paddled kayaks show their registration numbers on the stern (back) instead of the bow; again, it's best to check with local regulations before heading out onto the water.
If you plan on taking your kayak out onto public waterways often, registering it is a good idea. Not only does it ensure that everyone is following the same rules for safety and enjoyment, but if your boat is lost or stolen, having its serial number can help law enforcement return it to you quickly.