Safari 4: "Top Sites" - what does the white star mean?

Factual Questions
1

I recently upgraded to Safari 4, and I’m trying to figure out what something about the “Top Sites” feature. Every so often, one of the images of the different web-pages shows with the upper-right hand corner turned down, showing a white star on blue.

What’s the purpose of this?

2

It means the page has changed since the last time you visited.

3

That makes sense - thanks!