special portepee (knot), what unit

[m-e-h-t]

Hello, I've got this unissued knot within a nice Kriegsmarine lot.
It has the typical color of the seawater proof KM portepee, but what is the meaning of the black stripes?

Thanks for comments!

[m-e-h-t]

2

[m-e-h-t]

no one an idea???