One of the most commonly seen signs of coyote activity in the winter is yellow snow. This isn't just an indication that relief is needed from a full bladder. When coyotes pee, they are sending a message. It's a method of marking territory and saying to other coyotes, "This is mine. Keep out." Another coyote peeing in the same spot is effectively throwing down a challenge. How serious a challenge will be determined if and when they meet face to face.
Coyotes will use roads or trails as the edges of their territory and patrol them regularly to hunt for food and leave their mark. An observant walk or drive will often reveal these marking posts. When you find them, they are good places to do some targeted calling. It's a good bet that ‘yotes won't be too far away, and at this time of year they could come quickly to check out the source of any coyote vocalizations.
In the photo below, coyotes are using a basketball-size lump of snow thrown up by a rural snowplow as a territorial marking post.
Something else to watch for is signs of menstrual bleeding in female coyotes. Coyotes are monstrous, meaning they have only one breeding cycle per year. I'm not sure how long the females are in heat, but I suspect it's about 7-10 days, and when it happens both males and females are on the move. It's much like the whitetail rut, although in my experience, coyotes don't lose their minds like buck deer can. Where I live, in a cold, northern climate it's on during mid to late February. If you find a spot where a female coyote has been sitting on a snow bank, it's common to see blood spots where her butt was resting.
I took the above photo the other day, when I inadvertently pushed a couple of coyotes out of a slough bottom. The depressions in the snow show two coyotes sitting down and watching the world go by, with the female one bleeding. These two have apparently paired up. They weren't spooked too badly, so I tried to call them back, but with no success.
Reading tracks and signs is part of the fun in being outdoors. And as hunters, we're not just watching nature, we're predators ourselves, actually participating in the life cycle.