> Just the four letters D U N E, which are exactly the same shape but rotated 90 degrees.

This is what they went with for the movie posters too: https://upload.wikimedia.org/wikipedia/en/8/8e/Dune_%282021_... ...although, they cheated a bit with the E.

EDIT: Here is a better resolution: https://image.tmdb.org/t/p/original/2sxSn0jjjQoIIZfZjC6j5GZk... :)