The debit note is invalid without signature. The IOU is also a kind of loan contract. Since it is a contract, it needs to be reached out of the true intention of the parties. Without the signature of the parties, it cannot be proved that it is the true intention of the parties. If it cannot be proved, it cannot be proved that the contract is valid. Therefore, a debit note without the signature of the party concerned is invalid.
[Legal Basis]
In Article 143 of the Civil Code, a civil juristic act is valid if it meets the following conditions: (1) the actor has the corresponding capacity for civil conduct;
（2） True declaration of intention;
（3） It does not violate the mandatory provisions of laws and administrative regulations, and does not violate public order and good customs.
