I asked the RL development team about the exact purpose of the symbol and got the following answer:
the purpose of the icon is to pin Tracks. when you activate the object relative track function, it will automatically switch target's track according your selection, sometimes we want the specific track to show all the time, you can pin it with that icon, and the status will keep within the project, once you close the track, the pin track status will gone
Testing is fun, but quick correct answers are easier. :cool::smooooth: