Originally Posted by Zoot
That's almost certainly a second e-ink display, a tall thin one (larger version of the ones used on some memory sticks and similar devices as a capacity indicator).
Links are not selected directly when browsing a web page. You use the vertical thing to point at the approximate place on the page of your link and then it pops up a list of the links near that point from which you pick. So you don't have to scroll through them one by one on the page which would be slow even with partial refresh I think.
Can you provide the dimensions for the secondary display. The wiki describing the Amazon Kindle needs updating on this point.