Do old 100 dollar bills have water marks?

It would depend on your definition of old, if it's more than 15 years, then no. In 1996 the first major redesign of the U.S. $100 bill since 1929 took place, and added a watermark as a security feature. Bills printed prior to that date did not have a watermark. The watermark that was added to the bill shows a second image of Ben Franklin. Watermarks are created by varying the density of the paper during manufacture. When light passes through these variations, various tones of color are created.
Updated on Thursday, February 02 2012 at 12:37AM EST
Source: www.pbs.org/...