If you possess a completed or modified written instrument you know is fake and you do so with the intent to defraud or deceive another. In most jurisdictions, a forged signature is not legal under any circumstances.Forging a signature is considered a form of fraud. Forgery is a white collar criminal offense that involves creating a false written document with the intent to defraud. Forgery is a crime, not a civil matter. Go back to the police. The law defines forgery as the making of a fake document, the modification of an existing document, or the unauthorized signing of a signature. Forged documents are a form of document fraud in which authentic documents are altered or changed without legal authorization. A forged will is one of many forms of fraud. There are many different factors that may point to a will having been forged.