I followed the link to your website and found four pictures. They were all of the same pictograph, with a close up of a horizontal, thick, wavy line (equal guess would have been a snake) and three long, thin, unconnected lines going horizontal next to a large humanoid (one guess a shaman, could have been a chief, or maybe the head of household) figure. My initial reaction was, if it was a comet, why wasn't it depicted above the humanoid - suggesting up in the sky. Joe's suggestion that it's rain coming out of the clouds, imho, has stronger validity, although I don't necessarily think that is what is is either. The three thin lines are between the humanoid and another picture. The images may not be connected at all. Why do you think is is a comet?