Not sure what weapon you are referring to BUT I assume you mean a bladed weapon of some sort.
Swords and such are NOT concealed weapons and as such you can carry them IF they are IN their scabbard.
The issue is doing forms and exercises with them in a public place, the key word being PUBLIC.
First off, you really do NOT need that much room unless you are using a "pole" weapon ( spear, halbread, etc).
I know some forms can carry you all over the place BUT they all can be modified to cover less distance too, so...
BUT if you really want to be out in public and doing your stuff you really SHOULD be using wooden training weapons for no other reason than safety, forget the Laws for the moment, it just makes sense to be safe and to keep the public safe and you can find a wooden training version of every rigid weapon there is.
So...
Psalms 144:1
Praise be my Lord my Rock,
He trains my hands for war, my fingers for battle !