Answer:
Allusion
Step-by-step explanation:
An allusion is a figure of speech in which an object from an unrelated context is referred to in an indirect way. Through this allusion, the author wants the reader to understand different connotations that are additional to the literal meaning of the concepts. In this case, the phrase "jolly roger" is a reference to the flags that ships used to display when a pirate ship was about to attack.