sub-task indicator missing from JIRA card on Kanban board

[Jo-Lee Bertrand]

I used to have a little sub-task icon that showed on my jira cards (to indicate tasks with sub-tasks). It's now gone and I don't know what I did to remove it. The linked issues indicator is showing up fine. 

Note that I know how to configure the board to show sub-tasks on the card but this isn't what I am looking for. I am just sorting out how to return the indicator that seems to have vanished (screen capture of what appears to be missing is shown below).