The screenshot on the other post is from Prime, the icon is only visible on audio channels.
From the manual.
Create or Dissolve a Group in the Console
To create a Group in the Console, select the desired Channels and then [Right]/[Ctrl]-click and select Group Selected Tracks from the pop-up menu. To dissolve, or ungroup, grouped Channels in the Console, [Right]/[Ctrl]-click on any Channel in the Group and select Dissolve Group from the pop-up menu.
When an Audio Channel is in a Group, the Group icon appears on the Channel.
