A common way to tell if you have moisture problems in your basement, is the growth of mold on the walls and floors. In small quantities mold is harmless, but poses more of a threat as it grows. Some mold can cause allergic reactions while others can be fatal.
When mold is first spotted, it should be treated right away. If left alone it will grow and spread, potentially to other parts of the home. Inspect your basement paying close attention to areas with material such as plywood, drywall, furring strips, & carpet padding. Remember to bring a flashlight with you!
If mold is found do not touch it and do not breathe in heavily near it. If you do come into contact with it, wash your hands and clothes immediately. Mold is easily spotted by sight so you should not need to touch it.
Basement mold can be identified by its color, and ranges from light grey to black. It can also contain tinges of green, blue, or brown. If the mold is closer to black, then it is either the Stachybotrys or Cladosporium variety. Mold that is more grey, is either Aspergillus or Fusarium molds. These are good indicators of the type of mold at hand, but one can only be certain with professional help. Smaller patches of mold can be cleaned up by the homeowner, while larger patches should be left to the experts.
If mold is prevalent in your basement, consider waterproofing your basement to decrease the likelihood of future occurrences.