While current estimates put the rate of counterfeit $50 notes in circulation worldwide at less than 1 note for every 25,000 genuine $50 notes in circulation, if you end up with that rare fake, you will lose your hard-earned money. Counterfeit bills cannot be turned in for genuine ones, and knowingly passing along a counterfeit is illegal.
Easy-to-use security features help people check their U.S. money:
Watermark: a faint image, similar to the portrait, which is part of the paper itself and is visible from both sides when held up to the light.
Security thread: also visible from both sides when held up to the light, this vertical strip of plastic is embedded in the paper and spells out the denomination in tiny print.
Color-shifting ink: the numeral in the lower right corner on the face of the note, indicating its denomination, changes color when the note is tilted. For the new currency, this color shift is more dramatic. It changes from copper to green, making it even easier for people to check their money.