It’s just the new VS2012 icon for a pending Branch action. If you look closely, it’s not a ‘T’ but actually an upwards facing split arrow. A larger version of the icon can be seen if you look at the File -> Source Control -> Branching and Merging -> Branch menu item.
Normally you won’t see this since branch actions are usually performed server side. In your case since you didn’t have permissions it was tracked as a pending branch request, and cleared once your permission problem was resolved.