The program comprehension research community has been developing useful tools and techniques to support developers in the time-consuming activity of understanding software artifacts. However, the majority of the tools do not bring collective benefit to the team: After gaining the necessary understanding of an artifact (e.g., using a technique based on visualization, feature localization, architecture reconstruction, etc.), developers seldom document what they have learned, thus not sharing their knowledge. We argue that code bookmarking can be effectively used to document a developer's findings, to retrieve this valuable knowledge later on, and to share the findings with other team members. We present a tool, called Pollicino, for collective code bookmarking. To gather requirements for our bookmarking tool, we conducted an online survey and interviewed professional software engineers about their current usage and needs of code bookmarks. We describe our approach and the tool we implemented. To assess the tool's effectiveness, adequacy, and usability, we present an exploratory pre-experimental user study we have performed with 11 participants.