Final answer:
The icon used to mark favorite reports in a digital interface is typically the star, option a). This feature allows users to easily filter and access their preferred reports amongst numerous files.
Step-by-step explanation:
The icon indicated by the question is commonly used within digital platforms for users to label or highlight their favorite reports or content. The correct answer to the question is: a) Star. Typically, in many user interfaces, a star icon next to a report or file allows users to mark that item as a favorite, which then might be filtered or sorted based on this preference. This functionality is essential for users who need to access certain reports regularly amongst a vast array of data.