Calling a police officer "a badge" is an example of what literary device?

The phrase "a badge" used to refer to a police officer exemplifies synecdoche, which is a literary device where a part of something is used to represent the whole, or vice versa. In this case, the badge is a part of the police officer's uniform and identity, but it is being used to symbolize the entire officer. This technique helps to create a more vivid image or understanding in the listener's mind, emphasizing the officer's authority and role in society through a singular and recognizable aspect of their identity.

In contrast, metaphor and simile involve making comparisons, with a metaphor asserting one thing is another and a simile using "like" or "as" to make a comparison. Alliteration refers to the repetition of consonant sounds at the beginnings of words, which is not applicable in this context. Thus, the use of "a badge" to stand for a police officer demonstrates the concept of synecdoche effectively.