In the user control panel the option: "Mark all threads read on exit" would be very useful for some of us.
I've clicked "sign out" once in a while completely by accident. If I understand correctly, you want it to make threads read at that time?When log out, of course.
The explicit form we already have it. I use it whenever I leave this site
I have seen this feature in some phpBB-based forums, and I find it interesting, as it saves a few clicks to those who surf the forums in the same way as me.
Since it would be an option, it can be disabled by default.