Which of the following is a common sign of mold presence in buildings?

Unusual odors are a common sign of mold presence in buildings because mold often emits a musty or earthy smell. This odor can be an indicator that mold is growing in an area where moisture is present. Mold thrives in damp environments, and the odors associated with its growth can linger even after the mold is removed if not properly addressed. Identifying these smells can help in early detection, facilitating timely remediation and preventing more extensive damage.

The other choices do not directly indicate mold presence. Dry walls may suggest a lack of moisture, which would be an unfavorable condition for mold growth. Cold drafts relate more to ventilation and thermal dynamics within a building, while bright lighting does not correlate with mold presence at all. Instead, dark and damp conditions are more conducive to mold growth, making unusual odors the most relevant indicator among the options provided.