A web of agreements to protect the cash money system against forgeries. Try to buy certain printing equipment and you will be denied unless you are a nation state. Try to scan certain images and editing software will throw errors. Try to print a high-quality image and yellow dots will appear. It isnt nefarious. It is just countries protecting thier money supply.

But it is a conspiracy between nations. Thats why the same symbols appear on saudi, european, canadian and american bank notes.