marked without text

I noticed a little pin on the left side today, it says "marked without text" when I mouse over it. I searched the calibre site and forum and found no reference to this, nor on Google.

I'm sure it has something to do with the text search feature, which I love btw, but I don't know how to use this. And if it means I have books not searched yet, how do I force them to be catalogued.

Sorry if it seems if I went the easy route and posted this, but I did try to find the answer and maybe my google-jitsu is not up to snuff these days.