Which of the following is an example of information classification?

The option that represents an example of information classification is a government document marked as "Top Secret." This designation indicates that the information within the document is sensitive and requires a certain level of clearance to access, reflecting its classification status. Classification systems are vital in managing data that can potentially impact national security or sensitive operations. Documents are classified to protect them from unauthorized access, ensuring that only individuals with the proper permissions can view or handle that information.

In contrast, the other options do not illustrate classification. A report on historical events does not carry sensitive contents that would require classification and is generally accessible to the public. An open-access research paper is designed for wide distribution and is not restricted, further underscoring its lack of classification. A public safety announcement is typically shared openly to inform the community and lacks the restricted access associated with classified information. Thus, the document marked as "Top Secret" is the only example that explicitly shows the use of a classification system to safeguard sensitive information.