An offer by a merchant to lease goods to or from another person in a signed writing that by its terms gives assurance that it will be held open is not revocable, for lack of consideration, during the time stated or, if no time is stated, for a reasonable time; however, in no event may the period of irrevocability exceed three months. A term of assurance under this section on a form supplied by the offeree shall be separately signed by the offeror.