18 U.S.C. § 8: Obligation or other security of the United States defined

The term “obligation or other security of the United States” includes all bonds, certificates of indebtedness, national bank currency, Federal Reserve notes, Federal Reserve bank notes, coupons, United States notes, Treasury notes, gold certificates, silver certificates, fractional notes, certificates of deposit, bills, checks, or drafts for money, drawn by or upon authorized officers of the United States, stamps and other representatives of value, of whatever denomination, issued under any Act of Congress, and canceled United States stamps.