When the signature on the IOU is unknown and covered, but the corresponding conditions are met, it can be considered that the loan relationship is established and converted into a valid IOU. You can take the following ways:

First, the creditor directly claims the creditor's rights from the debtor or claims the creditor's rights through litigation, and the loan relationship is established when the debtor does not raise any objection.

Two, if the debtor raises an objection, you can carry out technical appraisal, signature or fingerprint can find that the loan relationship is established. In the absence of fingerprints and signatures, if there is other evidence to support it, a loan relationship can also be established.