In many a work of fiction nowadays we see the stereotypical ninja performing hand signs to perform a technique, signal his allies and what not.

Although I have only seen them in modern fiction (mainly popularized by anime like Naruto, but also seen in western fiction like videogames, series and cartoons) most of these hand signs are always the same, not changing at all from one work of fiction to the other, independently from studio, medium and so on.

The prevalence of these identical hand signs accross all mediums and stories has me wondering if they are based on real life accounts or techniques used by real ninjas.

Or if they are just a trope/cliché that has been copied in recent years by many sotrytellers because of the association these hand signs have with ninjas.