The signature of the guarantor of the IOU is invalid, mainly when the guarantor does not express his true intention. The guarantor's signature is invalid if the creditor and the debtor collude to defraud the guarantor to provide a guarantee, the creditor uses fraud and coercion to make the guarantor provide a guarantee against the true meaning, and if the guarantor's signature on the guarantee contract is forged by the debtor and the guarantor does not ratify it. Article 698 of the Civil Code Exempts the General Guarantor from the Warranty Liability. After the expiration of the performance period of the main debt, the guarantor of the general guarantee provides the creditor with the true information of the debtor's executable property. If the creditor gives up or is slow to exercise his rights and the property cannot be executed, the guarantor will no longer bear the warranty liability within the scope of the value of the executable property provided by him.