The current edition of the 'new' US $100 bill was released on 8 October 2013.  Today it cost approximately 16 cents to produce a single $100 bill, by far the most expensive bill the US has every produced with the most security features in history.   The majority of them are in foreign banks.   Its most distinguishing 'different' feature is also its most unique security feature, the blue security ribbon on the front.


3-D Security Ribbon
Tilt the note back and forth while focusing on the blue ribbon. You will see the bells change to 100s as they move. When you tilt the note back and forth, the bells and 100s move side to side. If you tilt it side to side, they move up and down. The ribbon is woven into the paper, not printed on it.


Before we discuss some other special features watch this short video:  https://www.uscurrency.gov/denominations/100

Bell in the Inkwell
Tilt the note to see the (Optical Variable Ink (OVI)) color-shifting bell in the copper inkwell change from copper to green, an effect which makes the bell seem to appear and disappear within the inkwell.  Also the numeral 100 in the lower right corner.



Security Thread
View the bill with an ultraviolet (UV) light to see an embedded thread running vertically to the left of the portrait. The thread is imprinted with the letters USA and the numeral 100 in an alternating pattern and is visible from both sides of the note. The thread glows pink when illuminated by ultraviolet light. All current bills have this feature (except the $1 bill), but in different locations and colors. Interestingly, the only two non-Presidents to be on current US bills are Benjamin Franklin ($100), and Andrew Jackson ($20); and the UV security thread on both their bills are to the left, whereas all the Presidents UV thread is to the right.




Watermark
Hold the note to light and look for a faint image of Benjamin Franklin in the blank space to the right of the portrait. The image is visible from both sides of the note.



Intaglio printing (/ɪnˈtælioʊ/ in-TAL-ee-oh; Italian: [inˈtaʎʎo]) is the family of printing and printmaking techniques in which the image is incised into a surface and the incised line or sunken area holds the ink.  It is the direct opposite of a relief print, where the parts of the matrix that make the image stand above the main surface.  You can see and feel the intaglio printing best on Benjamin Franklins jacket in the portrait.



EURion constellation (also known as Omron rings or doughnuts) is a pattern of symbols incorporated into a number of secure documents such as banknotes and ownership title certificates designs worldwide since about 1996. It is added to help imaging software detect the presence of such a document in a digital image. Such software can then block the user from reproducing banknotes to prevent counterfeiting using color photocopiers. According to research from 2004, the EURion constellation is used for color photocopiers but probably not used in computer software. It has been reported that Adobe Photoshop will not allow editing of an image of a banknote, but in some versions this is believed to be due to a different, unknown digital watermark rather than the EURion constellation.

There are numerous other, more common security features, such as micro printing, and tiny blue and red threads in the special paper from the Crane family currency printing process.



Many unique features to this new $100 bill that have references to Freedom, Independence and the Constitution.  Many deeply seated in our national founding, rich history and other curiosities, such as:
Independence Hall's bell tower clock
The time Independence Hall's bell tower clock on the front of the $100 bill before 2013 reads 4:10, a fact confirmed by the Fed and the Bureau of Engraving and Printing. The newer $100 bills released by the Treasury in 2013 show 10:30 on the clock.   Coincidentally:
  • April 10 (4/10) - is the 100th day of the year in the Gregorian calendar.
  • October 30 (10/30) - is the 303rd day of the year in the Gregorian calendar.
  • On 10/30 in 1735John Adams, American lawyer and politician, the 2nd President of the United States was born.  

Conclusion



In addition to the many normal ways to help detect counterfeit currency, and these enhanced special features, some currently found only on the $100 bill; there are allegedly 'restricted' or 'secret' security features.   One can only speculate what they might be...  perhaps the EURion constellation that prevents a counterfeiter from making high resolution copies also 'transmits an undetectable signal to alert the authorities'?  Or perhaps there are microscopic features hidden within the blue security ribbon?   Or maybe there are magnetic properties that, when scanned with special counterfeit detection machines, authenticates real bills?  We may never know.