Which of the following is an example of a document marking indicating proprietary data?

The choice indicating "For official use only" is an example of a document marking that signifies proprietary data because it restricts the dissemination of the information contained within that document. This marking suggests that the data is sensitive or confidential and should only be accessed or utilized by authorized personnel within specific settings or for designated purposes. Such markings help protect the integrity and confidentiality of the information and ensure that it is used appropriately within an organization.

In contrast, markings like "For public release" and "Free for sharing" explicitly permit broader access or distribution of the data, which does not align with the concept of proprietary information. "Internal use only" implies limited distribution within an organization, which could suggest some level of proprietary data; however, it does not convey the same level of specificity regarding authority and use as "For official use only." Thus, the choice that best exemplifies a proprietary marking is the one that clearly restricts access and usage to designated personnel or purposes, ensuring the information remains protected.