I'm not sure if you'll be lucky enough to ever have many of them, but the Federal Reserve says it will begin circulating a redesigned $100 bill in October.   The new bill will be packed with security features to make it very difficult to counterfeit.  The note includes a blue, 3-D security ribbon on the front that moves with the bill is tilted.  The inkwell and bell on the front of the bill, and the number 100 on the right-hand corner, also change from copper to green when the note is tilted.   It's only the 4th time in history that the $100 bill has been redesigned.

Fox News