WIBNI Terminator could watch for activity or silence in a specific shell (terminal? pane?)?
Both would set the urgent hint on the window when the condition is met.
"Watch for silence" is useful in the following scenario: Suppose you have a long-running job that produces output while it is running, for example building some software. Then it would be cool to select the "Watch for silence" action. This would continuously monitor activity in the terminal, and when no output arrives for some configurable time, it would mark the window as urgent so that it flashes in the Gnome taskbar.
"Watch for activity" complements "watch for silence" and is useful for long-running jobs that seldom produce output, and you want to be alerted when output happens. Perhaps "tail -F /some/log/file | grep SomePattern" is a typical example.
This ought to be possible with the signals that VTE provides.