Need help with some EKMS

[Daarom]

Hey guys. This is a very strange structure of ciphers and numbers. The roman 12 seems to be the Wehrkreis district. And the abbreviation SPK can in my opinion stand for Sprengkommando or Strassen Panzerkraftwagen Komp. Or maybe sparrkasse ? The letters BU SS could be from the manufacturer Bussing ? Doesn't look like a city to me. What is your thought on this. ?

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Dortmund Sprengkommando (SS-Baubrigade III) ???

[Daarom]

The ekm seems to have more of a civilian build than a military build?