Variable: org-task-overrun-text
org-task-overrun-text is an alias and customizable for
org-clock-task-overrun-text, defined in org-clock.el.gz.
Value
nil
Documentation
Extra mode line text to indicate that the clock is overrun.
The can be nil to indicate that instead of adding text, the clock time
should get a different face (org-mode-line-clock-overrun).
When this is a string, it is prepended to the clock string as an indication,
also using the face org-mode-line-clock-overrun.