It's a 1789 patern Imperial German Erkennungsmarke (also used during WWI).
Thank you kindzjal!
Wanted to clarify.
Correctly placed figures in the date of the year? 1789 or 1879?
The Prussian Army issued dog tags starting in 1870 during the Franco Prussian war, I think this style came out shortly after that so correct probably 1879.
Indeed Eike41 You are right, my mistake!