We've all seen those movies with guys who sheath their swords in an X style over their backs, why can't we do this in Arm? Only being able to sheath one sword or one bow on you r back isn't very realistic. I think a sword and bow would fit relatively well on your back, maybe we could even sling bows on our shoulders? All in all, I'm just saying we need more sheathing!
I suppose you could sheathe one sword over your back and wear the other on your back slot. I'm don't think you can draw from that slot, though.
If you are not wearing a pack or something like that, in other words, if your back location is empty, you can wear a weapon, and sheath a weapon. Which would be the same as X type sheathing in the movies.
I believe I won't spoil much IC information:
There are backsheaths in game that are worn on back and allow storing a weapon(s).
sheathe sword back
sheathe sword backsheath
...voila!
You can wear most bows I know on back, too.