When a storage area contains containers that hold, or have held, pesticides labeled with the signal words __________, warning signs must be posted on or around the storage area.

Posting warning signs when a storage area contains containers holding or that have held pesticides labeled with the signal words "DANGER" or "WARNING" is essential for ensuring safety. These signal words are critical indicators of the level of toxicity associated with the pesticides.

"Pesticides labeled with 'DANGER' signify a high level of toxicity and immediate harm, while those labeled with 'WARNING' indicate a moderate level of toxicity that could pose health risks upon exposure." Therefore, it is vital to alert individuals in the vicinity about the presence of potentially hazardous substances, thus ensuring proper precautions can be taken to prevent accidental exposure or accidents.

In contrast, labels with "CAUTION," "NOTICE," or "SAFE" may indicate lower risks or are not pesticides that necessitate the same level of protective signage. Thus, the requirement for posting warnings specifically targets the more dangerous categories of pesticides indicated by "DANGER" and "WARNING."