How to Spot Counterfeit Currency

1. The portrait is more lifelike than on counterfeit money.
2. There are fine lines, smooth and unbroken lines printed behind the president and behind the building on the reverse.
3. There is a polymer thread woven in the bill. The thread in the $100 bill reads "USA 100" and the $50 bill reads "USA 50". The thread can't be reproduced with copiers or printers but is visible when the bill is held up to a light or appears yellow when in ultraviolet light. Genuine bills also have red and blue threads embedded in the paper. On counterfeit money the lines look like they're printed on the paper but on genuine bills the lines appear to be in the paper.
4. There is a watermark or "shadow" to the right of the face on the bill. It isn't visible unless the bill is held up to the light.
5. Color shifting ink is used for the number in the lower right hand corner on the front of the bill. The ink appears green until the bill is held at an angle, then the ink looks black. The ink is also "never dry" ink, which means that it can be rubbed off. Sometimes; however, the ink on counterfeit money can also rub off. On the $50, the number 50 is printed in large print.
6. On the $100 bill microprinted words are written around the portrait. To the naked eye it looks like a black line but under a microscope the words "The United States of America" can be read. On the $50 bill, "50" is written around the portrait and "United States of America" is printed in Grant's collar.
7. Genuine bills have the Federal Reserve and Treasury seals. The saw-tooth points on the seal are clear, distinct, and sharp. The seals on counterfeit money may have uneven, blunt, or broken points.
8. Along with the seals on each bill there's a serial number printed in the same color ink as the seal. Numbers and letters are evenly spaced.

++In 2001, a man bought a sundae at a Danville, Kentucky, Dairy Queen with a $200 bill featuring President George W. Bush and received $197.88 in change.

++In September 2003, a North Carolina man named Travis Martin used a $200 bill at a Food Lion to purchase $150 in groceries; the cashier accepted the fake bill and presented Martin with $50 in change.

****Beginning with Series 2004, $10, $20, and $50 bills received a redesign with several changes to their overall look, notably the addition of more colors. Probably the most important new security feature is the addition of EURion Constellations (see right photo), a distinct arrangement of symbols or numbers which triggers many color photocopiers to refuse to copy the bill.
****The $1 and $2 bills have fewer security features than other denominations. This is seldom a problem because counterfeiters rarely try to make these bills--it's a lot of work for a buck or two!
****It's a common misconception that if the ink smears when you rub the bill on something, the bill isn't genuine. This isn't necessarily true, but ink that smears doesn't mean the bill is genuine, either.
****The Secret Service and U.S. Treasury don't recommend relying solely on a "counterfeit-detection pen" of the kind you often see clerks use in stores. These pens can only indicate whether the a note is printed on the wrong kind of paper (they simply react to the presence of starch). As such, they'll catch some counterfeits, but they won't detect more sophisticated fakes and will give false-negatives on real money that's been through the wash.
****"Raised bills" are a very simple type of counterfeit in which numerals are glued onto a low denomination bill to make it look like it's a higher denomination. You can easily spot these fakes by comparing the numbers in the corners to the denomination printed in letters at the bottom of the bill. If you're still not sure, compare the bill to another bill of the same denomination.
****The ink used in U.S. currency is actually magnetic, but this is not a method for detecting counterfeits. The strength is extremely low and is useful only for automated currency counters. If you have a small but strong magnet (such as Neodymium) you can lift a genuine bill. Although you cannot lift the bill off of a table, you can certainly tell that it is magnetic.