Off the the top:
[1] Lawful identification/credentials (motorist qualification card, lawful ID, etc.)
[2] IMHO car must be paid off*
[3] Sending to State DMV/DoR a Notice of Sale or Assignment of the automobile being sold or assigned to non-resident where most recently tagged - that lets the State know the car is no longer the previous owner's*
[4] Surrender plates if any associated with that chassis serial number (or VIN)
[5] Insurance or Financial Responsibility Bond*
[6] USDOT # showing no cargo, private, not commercial --notifying US Dept. Transportation that the # is only for helping law enforcement make distinctions betwen your private automobile and others; -- USDOT 3" or higher stickers on bumper and front bumper (license plate area empty or name of Entity or Person that the USDOT # is assigned and some artwork for fun)--anything about 'household goods' is to be avoided (see the link below);
[7] Private / Not for Hire stickers on the rear bumper*;
[8] not being a person born subject to the jurisdiction of the United States
One could even go as far as putting the VIN for the "Trade Name" or even filling a UCC or mechanic's lien on the automobile. IMHO * are mandatory or pretty much mandatory. IMHO it takes a reasonably well-rounded kit of knowledge and wisdom.
Regardless of that image, I would place separate PRIVATE / NOT FOR HIRE sticker on the bumper. USDOT 3" high letters minimum--to be read from a good distance. It is likely possible to get State tags with special arrangements at arm's length or better.