Dealer told me to forge a signature

You can sign for someone else if they authorize you to do so, either expressly or in some cases by implication (although the signature should more properly be in the form of "John Doe for Jane Roe") or if, after learning of your forgery, the person for whom you signed approves or "ratifies" the transaction.  If your fiance authorized you to handle the transaction, or just knew about it and didn't object, you should be ok.  If she didn't know that you were trading in the car, but learned later and doesn't object within a reasonable time, she will probably be deemed to have ratified the transaction.  This would protect you from any civil liability, but I don't know if it's a defense to a criminal forgery charge - probably it is. If your fiance does object to the transaction, she could theoretically file a criminal complaint against both you and the salesman.  On the civil side, she should not have any liability to the original seller, because the seller knew about the forgery from the beginning.  It is likely, however, that the seller is going to sell the contract, if it has not already.  If the company which buys the contract had no reason to know of the forgery, your fiance could (emphasize could; it's not clear cut) be liable to the assignee, but she would be able to compel you and/or the seller to reimburse her.