In 1972 the U.S. Federal government established the Hull Identification Number (HIN in this document), that is required for all boats manufactured or imported on or after November 1, 1972. Vessels manufactured or imported before this date are exempt from this requirement, when builder's identified boats ad hoc. The HIN is a 12 digit serial number that uniquely identifies a boat. It is analogous to a VIN on a motor vehicle registration. The HIN is normally used during the boat registration process and should be included on any bill of sale.
The primary HIN must be permanently affixed or engraved on the hull on the starboard side of the transom within two inches of the top of the transom, gunwale, or hull/deck joint, whichever is lowest, so that it can be seen from outside the boat. To identify a boats hull number for registration purposes some states may require a pencil rubbing or tracing of the hull number. To create a pencil tracing, place a blank piece of paper on top of the number and rub a pencil across the paper so that an impression of the number appears. If the rubbing is not clearly legible write the numbers you see adjacent to the rubbing and take a digital photograph.
Note: The HIN is not the same as a State registration number, which may be required to be displayed on the bow of your boat.