At http://www.fivedoves.com/letters/dec2013/garyn129-1.htm Gary discussed how Rev 1:20 calls stars "angels".  The word "angel" means "Messenger", so it is not impossible that this verse is saying that a star has a message.

How could a star tell a message?  What we call Astrology is a perversion of satan.  However, he tends to pervert something that has a basis in the real thing.  At http://www.levendwater.org/books/witness/the_witness_of_the_stars_bullinger.pdf is a copy of Bullinger's book, "The Witness of the Stars", in which he explains that God wrote the Gospel message in the stars, which is why Satan hates it so badly and why he has wanted people to see their personal fortune in the stars when God had a different message; not a personal messsage for a single person, but a broadcast for everyone.  If Godf has a personal message just for you, He'll deliver it in a personal way. 

If there is a message that a comet has for us, I suspect starting with Bullinger's book is a good starting point.  Trace out the path of the star/comet as it travelled through the constellations, and you might figure out what message it is saying by the way the moving star connects stationary stars whose meaning is already known.