My productivity can be seen in my portfolio, the contributions graph on my GitHub profile, my GitHub repos, the list of repositories I've contributed to and most recently in my contributions at NASA.
While I strive to be a "10x developer" on a team, and my contributions often show that, I don't like to use the term because it implies that working in isolation is the most productive way to work. But being a productive senior member of the team is about encouraging and enable other members of a team to be productive through mentorship, support and creating tools that make everyone's job more efficient.