You must have a valid NY State registration to ride your ATV in New York State unless it is only used for agricultural purposes or not-for-hire snow removal on private property.
What vehicles are considered to be ATVs?
An ATV is any self-propelled vehicle, including an off-road motorcycle, that is manufactured for use on off-road trails or in off-road competitions.  These vehicles are less than 70 inches wide and weigh less than 1,000 pounds.
What is my proof of ownership if I purchase an ATV from a private seller?