NO EXPERT I have seen many 37 mm shells embossed in this manner or in similar style Were they commercially produced for the civilian market?
They seem quite ornate to have produced under combat conditions
I have a several comments/ thoughts on trench art:
While some folks have a more stringent definition, most trench art collectors classify anything (utilitarian or decorative) made out of war refuse as trench art. There is no requirement that the object be made by a soldier or actually under combat conditions (in a trench).
A significant quantity of trench art was made post- war in larger commercial ventures; however, soldiers did actually make various objects during down time from combat. Trench art was a cottage industry during/ after the war, providing work/ income for soldiers and civilians alike; looking to feed the need for War souvenirs.
The craftsmanship of soldier and civilian makers varies. Soldier handy work and ability to create elaborate pieces is surprising to many. Remember, during the WW1 era, metal work and hand craftsmanship was not an unusual skill.
The type of work exhibited in this particular example certainly could have been easily created by a soldier craftsman.
For those wishing to see actual period documentation (photos, letters, etc...), I'd recommend Jane Kimball's book: "Trench Art: An Illustrated History".