'K': Not sure what I did to this one Usenet thread

So I'm using an older version of tin:
tin 1.6.2 release 20030910 ("Pabbay") [UNIX] (c) Copyright 1991-2003 Iain Lea.

There's one thread I'm participating in, and thanks to this one app I
use, I see that it's being updated with new posts. However, the posts
don't show up as unread articles...but they new ones do have a 'K'
next to them when I view them in the thread tree view, so I can hunt
them down that way.

Anyway, what does the K represent? Did I or somebody else somehow mark
this thread as something special? Is there any way of undoing it? I
skimmed through the man page but didn't know what term I was looking
for...

Thanks!
Kirk