Excuse me, is the iou valid only if it is signed, but not if it is fingerprinted?

You don't have to press your fingerprints to be effective. The following factors also affect the validity of IOUs: (1) The title says "IOUs". (2) state the reasons for the arrears, and illegal debts are not protected by law. (3) Write down the debtor's full name and ID number, and the debtor had better press his handprint. (4) The amount should be written in Arabic numerals as well as capital numerals, so as to avoid disputes over whether to tamper with it in the future; At the same time, the currency should also be stated. (5) write clearly the way of borrowing. (6) The term of arrears must be clear to avoid disputes over when to repay; It is best to capitalize. (7) The interest rate should be clearly written as annual interest rate or monthly interest rate, and should also be capitalized; Whether the interest rate after maturity is consistent with the agreed interest rate during the loan period is a common dispute, and the overdue interest rate slightly higher than the loan interest rate should be stated in the receipt. (8) "Take this as the basis" as the end of the IOU text.