Legal analysis: unsigned IOUs can be prosecuted. The details are as follows: 1, it doesn't matter if there is no debt in the payment, but it must be signed, either on the invoice or the receipt, or both parties can sign the contract, and there must always be a place to sign. If there is no signature or debt anywhere, it is broken. Only cash transactions need not be signed, just pay off the money and goods. If there is no on-site settlement, there must be written evidence, not necessarily IOUs.

Legal basis: Article 63 of the Civil Procedure Law of People's Republic of China (PRC). Evidence includes: (1) statements of the parties; (2) Documentary evidence; (3) Physical evidence; (4) Audio-visual materials; (5) Electronic data; (6) Testimony of witnesses; (7) Appraisal opinions; (8) Records of the inquest. Evidence must be verified before it can be used as a basis for ascertaining facts.