It's the naming prefix used by Rheinland NPC capital ships (go take a look). Its the same for LNS- and HMS- in that regard, while Kusari and Gallia player caps use prefixes that are different from the NPCs.
All of this stuff is voluntary, you can use whatever tag you want as long as it isnt owned by an actual faction or intended to be misleading (no using LNS- on your turtle).