Movie directors have a wide-ranging job set that spans across all aspects of production, essentially acting as a shepherd who must lead the film to the promised land. At the same time, as they go, they're hoping that they didn't take a wrong turn along the way.
When a film is being made by a sincerely talented director you can really feel it. They take control of the material in a way that lesser forces simply cannot and guide you as a viewer through the cinematic world they've created.
Sometimes, directors find a particular tool that especially suits them in their craft. Whether it be a visual flourish, a narrative device, or simply a stylistic choice, directors can become so fond of these tools that they become synonymous with the artist themselves. This is how a mere tool becomes a trademark: they present themselves time and time again throughout the director's filmography, becoming a thematic thread that ties all of their work together in a way.
These are the directors who have developed the most distinct trademarks over the years, that run through most or all of their work in one way or another.