Text boxes have leaders that can be changed to be different shapes. If your desired leader head (called Arrowheads in Revit) is not in the drop-down menu when you go to change the text type, go to Managed, Additional Settings and change it in Arrowheads first. Then you can go back to the text Type and change the leader type.
Timeline:
0:00 Intro
0:51 What NOT to do
1:13 What TO do
4:16 BONUS: How to change text color
5:13 Outtro