31 CFR § 601.2 - Distinctiveness requirement.

(a) The Secretary of the Treasury has adopted distinctive paper and distinctive counterfeit deterrents:

(1) In which the United States has an exclusive property interest; or

(2) That are not otherwise in commercial use or the public domain and are necessary for preventing the counterfeiting of United States Federal Reserve notes.

(b) The distinctive paper and counterfeit deterrents are used in United States Federal Reserve notes.