Final answer:
The hazardous identification number appears on containers or labels of chemicals and in safety data sheets (SDS) or material safety data sheets (MSDS).
Step-by-step explanation:
The hazardous identification number, also known as the NFPA 704 diamond, appears in two main places. The first place is on containers or labels of chemicals, where the diamond symbol is displayed to indicate the specific hazards associated with the substance. The second place is in safety data sheets (SDS) or material safety data sheets (MSDS), which provide detailed information about the hazards and safety precautions for handling the chemical.