to add to Steve's comment, Marx track is O27 profile, distinctively lower than standard O gauge height. i don't think i've ever seen Hafner or Flyer track that was anything other than standard O gauge height with much of it even banked. Lionel made very little 2-rail track. some of the others like Hoge or Unique Arts are also very distinctive and could not be confused with the light weight Marx track.
off hand, i'd say the chances of O27 style 2-rail track not being Marx is very slim.