This is a bookmark function. Click it and you can bookmark a post. Click it twice to clear it. It saves the post so that you can read it later and respond. You can find all of your bookmarks in your profile.
Click your profile image top right hand corner of the site (or placeholder if you did not upload an image)
You will see your name in grey underneath, then the ribbon, your private message notification and the gear.
Click the ribbon
They’re listed there