Do you need a separate bill of sale?
Required — MV-912, signed by both
The Vehicle Bill of Sale, MV-912, is signed by the seller AND the buyer, and New York requires it even when the vehicle is a gift. An acceptable bill of sale carries the year and make, the VIN, the date of sale, the purchase price, and the names and signatures of both parties. The buyer gives the ORIGINAL to the DMV when they title and register — so both of you should photocopy it first. That copy is the only one you will have.
Source: NY DMV, Buy, Sell, or Transfer Vehicle Ownership; form MV-912