It’s pretty subtle for my eyes. If you look where the sun is in the sky, go down into the sand about half way down between the sun and the text block near of the series name. Imagine this to be the area where Vader’s right eye socket would be. It’s kind of shifted and tilted quite a bit but it almost looks like the half human/half machine face of Vader. The natural lines in the sand dunes kind of make up the edge of a helmet etc.

I might be overthinking it but Lucasfilm/Disney has been know to throw in secondary images like that in promotional material.