WWI trench art?

Trench art is commonly defined as any decorative item made by soldiers, prisoners of war or civilians, where the manufacture is directly linked to armed conflict or its consequences.
Common articles that this includes are decorated shell and bullet casings and items carved from wood and bone.
To the uninitiated, all trench art, by definition, was made by a soldier sitting in a trench in France during the First World War, in the midst of a bombardment. To the cynics, it was all made in the 1920s by enterprising French and Belgian citizens. The reality is, naturally, a mix of these extremes, and everything in between, and spans conflicts from the Napoleonic Wars to the present day.