I found a picture with the kaiser wearing a skull

[siegersallee]

I cannot answer to the skull on the Lugers; but, the skull the kaiser wears is the uniform of the "Death's Head Hussars".

This totenkopf (or Totenschädel) was a symbol ingrained in the German Military as a symbol denoting elite status. The "Death's Head Hussars" of Prussia and Imperial Germany and the SS and the panzer corp of the Third Reich wore the totenkopf to indicate their elite status.

The most noted figure associated with the "Death's Head Hussars" was Field Marshal August von Mackensen.

In the photo below, he wears a similar uniform to the one the Kaiser wears in the photo in the previous post.

I am sure that, despite the subtle differences, both are the uniform of "Death's Head Hussars".

Richard