U.S. dollar bills have a number of non-obvious security features included to deter counterfeiting. The bills also contain some obscure imagery that has, in some cases, been connected with conspiracy theories and the occult.
As of 2015, the U. S. dollar bills made since 1996 contain a watermark that becomes more visible when the bill is held up to light. The ink used for the numeral on the lower-right corner of the face of the note also appears green when viewed directly but shifts colors to appear black when the bill is viewed from an angle. Security threads, which have the denomination engraved on them, are also embedded in the bill. The security threads of different denominations glow different colors when viewed under ultraviolet light. Microprinted lines that are not visible to the human eye also make the money difficult to copy and print with standard equipment.
The pyramid topped by an eye on bills' reverse side has sometimes been speculated to represent Masonic involvement. The written description of seal designer Charles Thomson indicates that the 13 rows of the pyramid represent the 13 original colonies, however, and that the Latin inscription refers to the poetry of Virgil. In addition, the right talon of the eagle on the front of the seal is considered dominant, so the placement of the olive branch there was done intentionally in the early 1800s to reassure Europe that the United States did not have belligerent tendencies.