100 US

From the BBC:
"US releases $100 banknote with new security features"

The US Federal Reserve has issued a new hi-tech $100 banknote comprising several new security features. It includes a blue 3D security ribbon and a bell and inkwell logo that authorities say are particularly difficult to replicate.  These combine with traditional security features, such as a portrait watermark and an embedded security thread that glows pink under ultraviolet light. The 2010 design was delayed because of "unexpected production challenges". The 3D security ribbon - which is woven into the note, not printed on it - features images of 100s that change into bells and move upwards or sideways depending on how you tilt the paper. Tilting also reveals a green bell within a copper-coloured inkwell to the right of the blue ribbon. In addition, the 100 number in the bottom right-hand corner shifts from copper to green. The redesigned banknote, which features a portrait of US founding father and scientist Benjamin Franklin, also includes raised "intaglio" printing that gives the notes a distinctive feel, and microprinted words that are difficult to read without magnification.Forgeries Over a decade of research and development has gone into the new note, the Fed said, in a joint project with the US Secret Service and the Department of the Treasury.  US authorities say that $100 bill is the most counterfeited of all US banknotes, but accurate figures for the total value of counterfeit cash in circulation are hard to come by. The US Secret Service estimates that counterfeit bills account for less than 0.01% of the $1.1 trillion (£683bn) of US money in circulation.

^ Hopefully, there won't be any issues with the new bills. Unlike many countries (that create a new currency and then force the people to exchange them within a certain time period) the US allows the old and the new bills to be used alongside each other - although if you go overseas you should bring only the new bills. ^

http://www.bbc.co.uk/news/technology-24431952