Legal analysis: the borrower's loan is invalid without signature; IOU is a contractual relationship, that is, a creditor's right relationship. In this relationship, there must be two parties, and an IOU belongs to both parties' contract and must be the true expression of both parties. Therefore, it can't be said that the borrower's real intention is expressed without the borrower's signature, so the contract, that is, the loan, is invalid and has no legal effect.

Legal basis: Article 490 of the Civil Code of People's Republic of China (PRC). If the parties enter into a contract in the form of a contract, the contract shall be established when the parties sign, seal or press their fingerprints. Before signing, sealing or fingerprinting, one party has fulfilled its main obligations, and the contract is established when the other party accepts it. A contract shall be concluded in written form as stipulated by laws, administrative regulations or agreed by the parties. If the parties do not do this in writing, but one party has fulfilled its main obligations and the other party accepts it, the contract is established.