German Ship Prefix's

As we all know that the prefix for all British ships of the line is "HMS" and for USA is "USS" so I got to wondering what the prefix for German ships of the line is/was/are.

I did a lil digging around and I get two types that seem to keep popping up, "KS" and "KM".

Now is "KS" for ships of the line (Navy) and/or "KM" for Merchant's or something else entirely.

I must admit I have never noticed a prefix for German ships in WWII which begs the question, did they even have 1 at all and if so what where an how?

Thx