What should alert you to the presence of dangerous goods?

The presence of dangerous goods can often be identified by certain warning signs, and a bag that is very warm or leaking is indeed a significant indicator. If a bag is unusually warm, it could suggest that it contains something hazardous that is generating heat, which poses a risk to safety. Similarly, if a bag is leaking, it raises immediate concerns about the potential for chemical spills or exposure to harmful substances, which can lead to fires, toxic reactions, or other dangerous situations.

While a small box with no label might raise questions, it does not provide specific evidence of danger on its own. A see-through bag allows visibility of the contents, which can help identify items, and a lightweight bag does not imply anything about the safety of its contents. These two situations do not prompt the same level of concern as a bag that is warm or leaking, which clearly suggests an issue that requires immediate attention.