If there are dark spots on your ceiling, floors or walls, this is a sure sign of mold growth. Musty odours and mildew are often also signs that mold may be growing in your property. Respiratory and allergy symptoms such as coughing, sneezing, trouble breathing and wheezing are a common indicator of mold growth as well. High humidity levels in your building that result in condensation on glass and metal surfaces are also a warning sign of mold.