If you know the key "counterfeit prevention" features of each U.S. bill, it is impossible for someone to use a counterfeit bill to pay you. Here are the key features for denominations of $5 and higher. The key to detecting counterfeit bills is to pay attention to the money you receive and take a moment to look for these features. The first 3 listed above are easily detected by holding the bill up to the light and looking for the shifting ink color with the naked eye. If a bill looks counterfeit, don't take it. You may call the Brevard Police Department if you believe someone has attempted or actually passed a counterfeit bill.
As you are looking at the portrait on the front of the bill, you will be able to see a watermark portrait on the right side of the bill that resembles to portrait on the bill when you hold the bill up to the light. Portraits face different directions for different bills, so make sure the portraits in the watermark and the face of the bill are looking the same direction. In some newer $5 bills, the watermark is a "5." The watermark is embedded into the bill and cannot be photocopied because it is not detectable on the surface of the bill. If a bill has been photocopied onto a different bill, the watermark will not match the denomination.
Each bill of $5 and above has a security thread that again, can only be detected by holding the bill up to the light. This security thread goes from top to bottom in the bill and has written on it the denomination and "USA." It cannot be photocopied for the same reason as the watermark: It is hidden inside the bill, not detectable on the surface.
Shifting Ink Color
The denomination number in the bottom right corner of the front of the bill is printed with two different ink colors. As you look directly at the number, the ink appears one color. As you turn the bill at a 45-degree angle, the ink appears to be a different color. This is because the first layer of ink is, in fact, a different color than the top layer. When you turn the bill at an angle, you see the side of the layer underneath, and you notice the other color. The number on newer bills appears copper as you look directly at the number, but the color changes to green as you turn the bill to a 45-degree angle.
Each bill has micro-printing that a copier is not capable of duplicating. Each border of the bills has fine scroll work that loses resolution when copied. There are also hidden phrases that are detectable only with magnification. As examples, the $5 bill has many of the names of the states in the facade of the Lincoln Memorial on the back, and the phrase "United States Of America Ten" is printed above the nameplate "Hamilton" on the portrait on the $10 bill.