If you sign the "IOU", you can sign the witness directly (or see the witness). For example, you can witness a loan and briefly explain the date, month and place. According to the relevant laws and regulations, if the parties conclude a contract in writing, the contract will be established when both parties sign or seal it. Article 490 of the Civil Code If the parties conclude a contract in the form of a contract, the contract is established when the parties sign, seal or press their fingerprints. Before signing, sealing or fingerprinting, one party has fulfilled its main obligations, and the contract is established when the other party accepts it. A contract shall be concluded in written form as stipulated by laws, administrative regulations or agreed by the parties. If the parties do not do this in writing, but one party has fulfilled its main obligations and the other party accepts it, the contract is established.