Rummaging through a collection of army shoulder titles and hat badges that appear to have been collected by my great-grandfather during his service in the Great War.
I was able to categorise all of them except this anonymous enigma:
Square brass badge with two lugs on reverse in the same manner as a shoulder title.
If you defocus your eyes from the four embossed "leaves" then the shape of a cross pattee becomes apparent. Surmounted by a Tudor crown.
And the winner is...
Once again Brian C wins the Google-Fu Trophy by identifying this as the badge of the Army Chaplains Department. From some examples on the Web, it seems that it was common to blacken them with paint to prevent glinting.