Well, I'm going to use this site as an example: link Every time you move the mouse towards the close the tab button (or just click on it - whoever you like, you can test by opening any site link in a new tab and access it by the keyboard shortcut [Alt + tab number] and then position the cursor over the close button ), which appears a div suggesting inscription in the feedburner. I have seen this on other sites too, but in my searches I did not find anything related.
Thanks in advance!