It could be seen somtimes when I surfing Ask Ubuntu that something different on the title of my web-browser, which is '(', number, and ')' such as (2).
'(2) Ask Ubuntu'
'(1) Ask Ubuntu'
It is the number of new questions since you last refreshed the page.
This can be done either by reloading the page (e.g. with F5 in FireFox) or by clicking the grey
X questions with new activity banner above the question list. Note that the second option does only load new questions, but does not actualize the state (votes, views, answers...) of the already shown ones.