When I'm on Super User, I often see that there is a count in the first opening tag. There is no counting on other sites, I thought that this waS Firefox problem then I opened it in Google Chrome and saw the same issue.
It's showing you the number of updated posts since you last looked at that page. If you click back, you can see a grey button that will show that same number. You can click it and it'll load in the updated posts inline.