Under New York Law, a "forged instrument" means a written instrument which has been falsely made, completed or altered. First, you must possess an instrument that you know to be fake whether it is falsely created, changed, altered, etc.Criminal possession of a forged instrument is a legal charge that falls under the broader category of forgery and fraud offenses. Forgery in the Third Degree, New York Penal Law 170.05, is a misdemeanor crime that carries a sentence of up to one year in jail. Forgery, deceive or injure another, he falsely makes, completes or alters a written instrument which is or purports to be.