Which statement reflects the role of signal words on pesticide labels?

Signal words on pesticide labels serve as essential indicators of the product's toxicity level and potential hazards associated with its use. These words, which typically include terms such as "Caution," "Warning," and "Danger," are crucial for ensuring that users are aware of the risks involved and can take necessary precautions to protect themselves, others, and the environment.

The presence of these signal words helps in quickly conveying the severity of the product's potential toxic effects, thereby guiding applicators in making informed decisions about handling, application methods, and necessary safety measures. This aspect of labeling is fundamental in promoting safe and responsible pesticide use, reducing the risk of incidents related to exposure or accidents.

The other options do not accurately describe the function of signal words. For instance, while effectiveness and registration details may be important, they are not directly tied to the explicit communication of toxicity risks that signal words provide. Similarly, using them for marketing purposes does not align with their primary role in safety and caution. Thus, the indication of toxicity through signal words is what makes them a vital component of pesticide labels.