I recently asked a question that was not closed as a duplicate and a few days later it appears to me that it has been "linked" to another question that is relevant. That is, on the right side of the screen on each of the two linked questions, just above the "Related" links, there is the link for the "Linked" question which directs to the other one in each case.
How can I add that to a question? Do I need a specific badge for that? If yes, and I don't currently hold it, what is the accepted manner of indicating that two questions need to be linked? (e.g. post a comment under the original question with the link for the other one?)