The swords will have very intricate designs on the handle and most will have bronze scabbards. The average length is 39 inches for a katana. Each of the swords I have evaluated in the past have had locking mechanisms on the handle to attach to the scabbard. You will want to check for the signature or name on the blade.
World War II vintage Japanese swords are valued in terms of quality, craftsmanship, and provenance. Many American soldiers took swords home as souvenirs from battles in the South Pacific theater of the war.
High quality and valuable Japanese swords are much more ornate than regular battle swords. The hand carved handles and etched blades were carried by people with much money but little to no battle experience.
Often WW2 swords used by the Japanese were handed down and were orginally made during the reign of the samurai. A emblem can be often found at the base of the blade and with some skill it can be determined who and where it was made.