All sites in the network have a blurb at the top, telling visitors what the site is all about:
"Stack Overflow is a question and answer site for professional and enthusiast programmers. It's 100% free, no registration required."
"Programmers Stack Exchange is a question and answer site for professional programmers interested in conceptual questions about software development. It's 100% free, no registration required."
However, this description is not visible for logged-in users and I cannot find this text anywhere once I'm logged in.
I sign up for an SE site whenever I see a useful answer I want to upvote or just to leave a comment, thus I currently have 41 accounts. The problem is that I often forget what each site is exactly for and whether or not I should mark a post as off-topic.
Having a way to enable the site topic blurb or at least adding it somewhere where it can be seen during the flagging process (perhaps only the off-topic section) would be most helpful.
Perhaps it would also suffice to just keep the banner for new users, and have them close it once ("don't show this again") after they've signed up. At the moment, after you've signed up there is no mention of what the site is about. For most of my accounts, I've never even seen the blurb.