You'll most likely smell a skunk before seeing one. They tend to leave a slight stench in the areas they frequent during the day, even if they do not spray in your yard. If you smell skunks in the late winter, it's conceivable that neighboring males are competing for female partners.
Round, shallow holes that are completely circular are another evidence of skunks on your property. Skunks are special in that they only dig deep enough to find grubs and other insects that live in the dirt. It's possible that they'll leave tracks in the loose earth. These footsteps resemble those of a cat, however they have five toes instead of four.