For the problematic "hiss" in the KJV, Gileadi translations "summons." The NIV uses "whistle" which retains the sound connotation while preserving the idea of a "call." Thus the Lord raises the ensign, and calls to all nations.
The coming of the judgement of the Lord may begin in destruction of the old, but it will be an ensign to the righteous. The theme of the ensign reprises the opening of chapter 12.
Translation analysis: the ending phrase: "none shall be weary nor stumble among them," is the opening phrase of the next verse in the corresponding KJV Isaiah text. The verse markings are arbitrary, and the location of the phrase at the end of 26 or the beginning of 27 makes no difference to the reading of the text.