When transporting hazardous materials, how must they be identified?

Hazardous materials must be properly identified to ensure the safety of everyone involved and to comply with regulations set by agencies such as the Department of Transportation (DOT). The correct answer highlights that hazardous materials must be clearly labelled. This labelling includes specific symbols, warnings, and descriptions that inform handlers and first responders about the nature of the materials being transported, their risks, and the necessary precautions for safe handling. Each label involves specific colours and design elements that standardize the communication of hazards, making it clear what risks are associated with the materials.

Other methods of identification, such as marking with stickers or outlining in specific colours, may be part of the overall strategy for material safety but do not fulfill the comprehensive requirements necessary for transporting hazardous materials. Securing materials under lock is more related to preventing theft or unauthorized access rather than providing the necessary identification required by regulations. Proper labelling is a crucial component in maintaining safety standards during the transportation of hazardous materials, which is why it is emphasized as the correct answer.