That is a tough one! Lots of Highlanders went to the central part of Scotland for work, my father and grandfather included. I can imagine that a fair haired fellow named Alexander might get nicknamed Alasdair Ban by a Highland co-worker, pal or school mate. This Alexander might then sign an autograph book that way, but not spelled correctly if he himself was not a Highlander or familiar with Gaelic words. Highlanders loved to give everyone nicknames. You were lucky if your main feature was blond hair, hence Ban, and not someone with a stutter, a limp or a drinking problem!
In days gone by, nicknames were almost necessary. With the traditional naming pattern, a man named Alexander would in theory have one son named Alexander and each of his sons would name their eldest son Alexander too. You can imagine that there might be several men with the exact same name in one area and so the nickname sorted that out - Big Alec, Young Sandy, Red Alasdair etc., all in Gaelic of course. Trouble is none of that was written down on records. My father, at 6 ft. 2 in. tall, was known as Innes Mór or Big Angus, in his youth.
Mary