TortoiseSVN uses up to seven overlay slots for the status:
svn:needs-lock property on a file, Subversion makes that file ReadOnly until you get a lock on that file. Read-only files have this overlay to indicate that you have to get a lock first before you can edit that file.Unlike TortoiseCVS (the CVS shell integration) no overlay icon for unversioned files is shown. We do this because the number of icon overlays are limited system wide and should be used economically.
In some situations the overlay icons may not appear. This can happen on older Windows version (before Win2K) or if other applications install overlay handlers as well, since overlay icons are a limited ressource in Windows.