Since the birth of the first paper currency in the Song Dynasty, counterfeiters have emerged one after another. According to the "History of the Song Dynasty", within less than 20 years of its issuance, "fake Jiaozi" had already appeared on the market, disrupting the market economy and causing local transportation officials to "want to abolish it". The Song Dynasty government first started with raw materials - only Sichuan paper made from hemp bark was used as raw material. The ancient people referred to the paper currency made from this type of bark as "bark coins" or "bark coupons", and at that time, only the imperial court had control over the origin of this bark. The paper currency made from shredded paper has a high quality and can be compared to non counterfeit paper currency, making it possible to identify the authenticity of the currency at a glance. But with the development of folk technology, soon this problem has been overcome by counterfeiters. So in the Yuan Dynasty, it went further and defined the private purchase of paper for making banknotes as a major crime. According to the "Travels of Marco Polo", the paper used for the Yuan Dynasty's banknotes was mulberry bark paper, which not only had distinct ink patterns and was difficult to imitate, but also punished those who privately purchased it with extreme punishment. In addition to solving problems from the source, ancient people also attached great importance to anti-counterfeiting printing of paper currency. As early as the Tang Dynasty, the people of Chengdu had invented "water pattern paper" with two types of printing: clear and dark, which other regions could not produce at all. The watermark anti-counterfeiting technology on modern banknotes originated here. The Liaoning Museum houses an old version of Jiaozi from the Northern Song Dynasty, which was printed by Qing Dynasty researchers using the original printing plate used to make Jiaozi. Currently, there is only one such piece in China, and it is the only physical material for studying the development history of paper currency in China. Its vertically elongated layout is divided into three parts, with ten square hole round coin symbols at the top, highlighting its currency attributes. In the middle, there are 29 neatly arranged characters: "Except for Sichuan, Xu is in charge of public and private affairs in various provinces and counties, and is also in charge of the circulation of 770 taels of money." The approximate meaning is: "Except for Sichuan, official and private transactions are allowed in various provinces and counties, and those who handle the money will consider it as 770 taels of money and circulate it." In just 29 characters, the circulation area, occasion, and currency value are specified. The lower part is engraved with Song Dynasty folk paintings, which were the "anti-counterfeiting marks" at that time. The patterns on ancient banknotes were often extremely complex and exquisite. The pattern on the ticket is usually carved with intricate details such as houses, trees, and stories of characters, with complex lines, known as "house wood characters". Carving such patterns requires superb skills and the difficulty of imitation is extremely high. The color of printing can also be used to achieve anti-counterfeiting. In addition to the common red, blue, and black color schemes, overprinting pattern patterns can form multi-color tickets that are difficult to replicate, with strong anti-counterfeiting performance. More importantly, a large number of official seals are affixed, including the seals of issuing institutions, saddle seals, denomination seals, brand seals, and so on. It is almost impossible for counterfeiters to forge the seals and colors of so many different stamps at the same time. Ancient paper currency often had secret codes, flower seals (special symbols for signature and painting), or secret codes printed on the face, which only official insiders knew their meanings and served as the key to verifying authenticity. In addition, there will be regular updates. Every two to three years, a new edition of Jiaozi will be issued, with redesigned and replaced designs, texts, seals, and secret codes, and the old version will be invalidated. This greatly shortens the time window for counterfeiters to study and replicate, effectively reducing the risk of long-term forgery. These comprehensive measures, under the technological conditions at that time, constituted a fairly rigorous anti-counterfeiting system. (New Society)