Which of the following is not an example of a nonverbal signal?

The volume of voice is indeed the correct answer here because it is considered a verbal signal rather than a nonverbal one. While the way people speak, including how loudly or softly they project their voice, can convey meaning and emotions, it primarily involves the use of language.

In contrast, facial expressions, body language, and gestures are all forms of communication that do not rely on spoken words but instead operate through visual cues and physical movements. These nonverbal signals play a crucial role in expressing feelings and attitudes and can often enhance or contradict verbal communication. Understanding these distinctions is essential for interpreting messages accurately in various communication contexts.