Vehicles have a state document of title. Normally, the donor endorses the document of title. The non-formal letter or deed of gift is a document of the donor's intent to make an irrevocable transfer. This document should indicate the year, make, model and mileage for the vehicle, the condition of the body, and general mechanical condition. It also is nice to have a photo that shows the condition. See example of such letter here - http://www.giftlaw.com/glawpro_subsection.jsp?WebID=GL1999-0110&CC=4&SS=3&SS2=2#Link5. The letter should be signed and signature notarized.
A vehicle with a current lien must have a letter of permission on the lien holder’s.