The whole stamping thing seems quite impractical. Also, some people might choose...to not stamp scrips? How often can you stamp a bill?
Also, this creates information not only for the Towers, but any spies. They only need to look at the stamps to assembles a network of economic exchange, which can be used against Leaf for an economic attack.
Nevermind. I didn't realize the idea was to use the scrips as stamp.