Signature can only determine the approximate time now. Formally, a signature is a trace formed on a document by the signer using a writing tool. With the passage of time, the ink used for his signature will have corresponding physical and chemical changes. By detecting the degree of change, we can know an approximate formation time. However, due to the limitation of the existing detection technology or means, there will be some error between the detection results and the actual formation time, and the general error is 2 to 3 months. And if it is necessary to detect the formation time, there will be some conditions. However, with the progress of science and technology, the detection technology and means will be further improved, and the determination of the formation time will be more accurate.