Only sign the ID number, and the letter of guarantee filled out by others will be valid. According to the relevant laws and regulations, only signing an agreement without fingerprinting has legal effect, and signing has the same legal effect as fingerprinting, which has little to do with the identity number. According to the relevant provisions of the Contract Law, the parties have corresponding capacity for civil rights and capacity for civil conduct, and enjoy the right to conclude a contract voluntarily according to law. The content of the contract does not violate the law, and there is no situation in which the contract is deemed invalid according to law. The contract is legal and valid. Guarantee refers to the responsibility provided to creditors by individuals or entities to ensure the performance of others' debts. The guarantee can be property mortgage or personal credit guarantee.