After upgrading the client from Subversion/TortoiseSVN 1.3.x to 1.4.x some unversioned files display green checkmarks instead of no overlay icon at all.
It looks like something is left behind during the upgrade which confuses the TortoiseSVN status cache.
The standard procedure to resolve this problem is to close all explorer windows that display the working copy in question and to kill the TSVNCache process. When the explorer window is opened again, the TortoiseSVN status cache wil rebuild its internal data structures.