N.Y. Pers. Prop. Law § 313
No guaranty given to the seller or to the seller and the seller's assignee of the liabilities of a buyer under a retail instalment contract shall be valid unless the guaranty is incorporated in or endorsed on the contract or identifies the contract and specifies the time balance thereof or, if the guaranty relates to one or more future retail instalment contracts, it limits the liability of the guarantor to contracts dated within a period of two years from the date of the guaranty and sets forth the maximum amount for which the guarantor shall be liable. A copy of the guaranty shall be given or mailed to the guarantor upon or immediately after the execution and delivery of the original guaranty by the guarantor.
As used in this section, "retail instalment contract" and "contract" include a retail instalment contract as defined in the retail instalment sales act, constituting article ten of this chapter. This section does not apply to a guaranty made by a seller or a holder of a retail instalment contract.
N.Y. Pers. Prop. Law § 313