Get the proper bag to carry your sword. Here in Japan people attend various types of sword classes, and kendo supply stores sell bags for shinai, bokken, and genuine swords. You are not allowed to carry any of these in public unless they are zipped or tied up in one of these bags. They are not expensive, $20 will buy a decent one. A case for a golf driving club will also work. The cases are meant to be carried slung over your shoulder. They are comfortable enough, but if the case moves around, you can add a second strap which goes around your waist, that will keep it steady.