If Windows is Suddenly Missing Overlay Icons ...
It's one of those days. You boot your trusty device and all you overlay icons for such unimportant things as TortoiseSVN/Git and Dropbox are missing. Yippeh kay yay!
I'll bet you something valuable that you installed or updated something during you last session which registered further overlay icons in your Windows installation. And that is exactly the problem: Windows (due to some weird legacy shit) can only process a maximum of 15 overlay icons globally, if that number is surpassed none are shown.
To solve this you might have to do three things:
1. Open regedit and go to HKEY_LOCAL_MACHINE/SOFTWARE/Microsoft/Windows/CurrentVersion/Explorer/ShellIconOverlayIdentifiers where all registered icons can be found and delete unneeded entries until you got 15 again.
2. You might have to reinstall TortoiseSVN/Git (but only one of them, since the use the same icons).