The German ships have not had any prefixes since the Kaiserliche Marine:
SMS = HMS....but there have been no official designators such as DKM or BMS except in some of the English literature and by some model makers.
Most of these had been actively involved in sinking German ships and u boats in WW2. When transferred the British Admiralty would have had no say in the choice of new names. And rightly so.
All western navies maintain a policy of keeping their rich traditions of ship names and their honours alive. Some names will really get up other Countries noses. So be it. Germany must be no different. U boats are still numbered, that is tradition. And unique.
A full broadside. The traditional English salute. Thanks. Sean.