westof30 Not sure if this is the answer you're looking for, but if you mean how do you mark all communications (in your inbox) as read, check the "unread only" box at the top of the inbox, and everything that you've already read should disappear. The link for "Mark all read" will go active only when you've received a new inbox posting, and it can then be used to mark the new post as read without reading it.
Now, as for marking all forums read,
I'm not sure there is a way to do that. But I guess I'm not really understanding why you'd need to since your inbox preferences and the filter tabs on your activity page allow you to screen pretty much everything except new discussions, posts, messages, and alerts about followed content or from your connections or groups. That is, providing you use those two pages to navigate rather than scrolling through and perusing each forum. I certainly don't have the time (or the desire) to do the latter. -->