Try this link:
<your site>/mod/forum/index.php?id=xxx where xxx is the ID of a course.
Here is the Moodle.org equivalent: https://moodle.org/mod/forum/index.php?id=5
In one click you can subscribe/unsubscribe to all forums in a course.
I'm sure Mary or Helen will have a way to find this link in the menus.
-Derek