WW1 German 25cm s. Spr markings

[MINENAZ16]

Hello,
Documentation on 25cm s.Spr projectiles markings are scarce.
Lot of ww1 pictures show shells without markings.
The nice picture below shows a "too beautiful (?)" shell with Rheinmetall markings.
Does anyone know the German doctrine for markings ?

 

[Der_Feldgraue]

It seems to be very difficult to find such details except those from old photos. Its also interesting to note, that all "Wurfminen" were not considered as artillery in german manuals and regulations but as engineer equipment, so their markings are completely different to artillery shells.