Haley's Comet Predictions and Mark Twain?

Mark Twain was born with the approach of Haley's Comet and died when it ped again. He was aware of this fact. I have read an inscription in one of his books that predicted 1957..initals t j or j j and g m a and the year 1957. Does anyone have a clue as to what this could mean..?? did he write any other Star or Comet predictions anywhere. I thought maybe it was about Haley's but maybe some other meaning since Haleys Comet ped here again in 1986.