1. It is best to have the borrower's ID number on the IOU, which can ensure the safety of the loan, but the ID number is not a necessary condition for the IOU to be established and valid; Without the ID number, the IOU has other terms, and the IOU has the same legal effect; The ID number is only for locking the borrower's identity more conveniently, quickly and safely.
2. The borrower's signature of the IOU takes effect. Because people's handwriting can be recognized, people's handwriting is unique like fingerprints, so it is impossible to imitate it completely, and it is unique and exclusive. If the borrower denies the fact of borrowing money, it can confirm the relevant facts through handwriting identification.
3. In fact, even if there is an ID number, if the borrower denies that the ID number was written by himself, handwriting identification will eventually be carried out.
Legal basis: Civil Code of People's Republic of China (PRC).
Article 667 A loan contract is a contract in which the borrower borrows money from the lender, repays the loan at maturity and pays interest.
Article 668 A loan contract shall be in written form, unless otherwise agreed between natural persons.
The contents of a loan contract generally include terms such as loan type, currency, purpose, amount, interest rate, term and repayment method.
Article 669 When concluding a loan contract, the borrower shall, at the request of the lender, provide the true information about the business activities and financial status related to the loan.