How can you tell if a 1950 US 20 dollar bill is fake?

Before the 1990s US bills didn't have a lot of anti-counterfeiting features. A 1950 bill won't have a watermark, microprinting, value strip, the Words In God We Trust, or color-shifting ink just to name a few things so don't even try to find them.

The best feature to look for would be the tiny red and blue fibers that are mixed into the paper when it's manufactured. Also, the teeth on the treasury seal will be very sharp and uniform in shape on a real bill. The engraving of Hamilton's picture will be crisp and clear as well.