Which functionality of Autopsy extracts web history and bookmarks from browsers?

The correct choice is based on the specific capabilities of Autopsy, which is a digital forensics platform. In the context of extracting web history and bookmarks from browsers, the term "Web artifacts" accurately represents the type of data that Autopsy can analyze.

Web artifacts encompass various data types related to web browsing activities, including history, bookmarks, cached pages, and cookies. These artifacts can provide crucial insights into a user’s online behavior and activities, making them essential for investigations that require uncovering the web usage patterns of a subject.

The other options refer to different aspects of digital evidence collection and analysis. For instance, operating system artifacts generally pertain to data stored by the operating system itself, such as system files and logs, rather than browsing history. File signatures are related to identifying file types based on their content rather than extracting specific user data. Network metadata deals with data packets and traffic analysis, which does not directly provide access to web browsing history or bookmarks.

In summary, "Web artifacts" specifically refers to the functionality that allows the extraction of browsing history and bookmarks, making it the correct choice in this scenario.