Recently I had an annoying issue: C# project checked-in into TFS was added to Visual Studio 2012 solution and was lacking TFS status icon in Solution Explorer:
Turns out the fix to this issue is very simple:
- In VS2012 Menu go to File > Source Control > Advanced > Change Source Control
- In Change Source Control window select project that was missing TFS Status icon, it has Not Controlled status
- Click Bind
- Save your solution and check it in into TFS.