Comets have long been regarded as omens of extraordinary portent. Novae, eclipses, conjunctions, anything seen in the sky can serve in this role, but bright comets have always held a special awe.
Even today those who seek signs are quick to seize upon any unusual astronomical event. A few months ago it was meteors, events over Chelyabinsk grabbing the attention. With ISON entering the inner solar system the attention shifts.
Bright comets are invariably seen as omens by some. History is littered with stories of comets and prophesies. This has not changed, there are many recent examples… Hale-Bopp, Hyakutake, Elenin, each has been used to make all manner of wild predictions. Comet C/2012 S1 ISON certainly fits the role. It will most likely be quite bright, easily visible without optical aid. It may even be visible in the daytime.