An appearance of so many (four) comets at once is a rare thing: Four is the number of the created world, of matter itself. So this IS a timely harbinger! And possibly an exciting message for us...

   The meanings per research are in ( )... 

  Dates all center around the 18th.  Nov. 15-18 when Comet LINEAR X1 passes by the bright star Arcturus (He cometh), Nov 17-18 when Comet ISON has a close encounter with Spica (the Church), and Nov. 18-20 when Comet Encke buzzes Mercury (swift/messenger/intellect). Meanwhile, bright Comet Lovejoy is "approaching" Ursa Major (the Larger Sheepfold). Possible interpretation "He cometh for the church swiftly/cleverly". The larger sheepfold could be the innumerable multitudes of tribulation saints. And then world judgement as both the Sun and then Ison pass dead center through Libra (the Scales) in late Nov.

Research/sources;

Spaceweather.com

J.A. Seise: "the Gospel in the Stars"

E.W. Bullinger: "the Witness of the Stars"

Wikipedia: Mercury (and various other sites)

Andy H. Stellarium (Ison and Sun trajectory)