If someone owes money and doesn't pay it back, his wife can sue together if she doesn't sign it. If the debtor's wife doesn't sign the IOU, they can also sue together.

Article 41 of the Marriage Law: At the time of divorce, the debts originally incurred by the husband and wife living together shall be paid jointly. * * * If the same property is not paid off, or the property belongs to each other, it shall be paid off by mutual agreement; If the agreement fails, the people's court shall make a judgment.