If there is only a signature but no handprint on the IOU, it will not affect the legal effect of the IOU. As long as there is a real creditor-debtor relationship between the two parties, and the content of the IOU is enough to prove the creditor-debtor relationship between the two parties, then generally speaking, the IOU is legally effective.

The IOU must have a real loan relationship as the background, and the IOU has the official signature of the borrower. Even if the IOU is not fingerprinted, such IOU is protected by law. The creditor shall keep it properly and pay attention to prompt notice within the limitation of action.

Required contents of legally effective IOUs:

1. The legal full names of the borrower and the lender shall be clearly written;

2. The loan amount should be clearly written, including the amount expressed in words and figures;

3. The term of the loan should be clearly written, including the start and end dates of the loan and a clear loan term;

4. The specific repayment date should be clearly written;

5. The loan interest should be clearly written, and there should be a clear annual interest rate or monthly interest rate, as well as the final loan interest payable (including the amount expressed in words and figures) and other agreements;

6. The date, month, day, time and payment method of repayment of loan principal and interest shall be stated;

7. There should be the borrower's personal signature, handprint or handwritten signature.