Prussian button
 

Can anyone please tell me who specifically wore this type of button? It is different from the generic Prussian type worn during the Great War.

A similar button can be found in the Prussian section of this page. (You will have to scroll down).

http://www.colchestertreasurehunting...ignbuttons.htm

It is the 'minor coat of arms' and it was worn by most uniformed state servants on their daily uniforms. The German Empire was highly militarised and many services, e.g. mail, railways etc. were state operated.
Your button has Wilhelm II's monogram on the eagle's chest.

Many thanks for sharing your knowledge, it is appreciated.

Simon