Final answer:
In UML notation, the guillemets character is used to show stereotypes, which provide additional meanings or properties to UML elements.
Step-by-step explanation:
In UML (Unified Modeling Language) notation, the guillemets character (<< >>) is used to denote stereotypes. Stereotypes are a mechanism in UML to define additional meanings, attributes, or any other kind of property that can be attributed to some UML elements. For example, if you have an action in a use case that is an extension of another action, you might see it annotated with guillemets as <>. This helps to provide a further layer of specification and clarifies the role that the specific element plays within the model. Therefore, in the given options, 4) stereotypes is the correct answer.