Currently there are three basic icons - read-only (locked), modifiable (unlocked), and modified (locked or unlocked). I propose that there should be separate icons for the modified states, based on whether the file was unlocked or locked before modification.
Three seems a bit low to me. These are the icons that TortoiseCVS use:
Conflict
Changed
NotInCVS
InCVS
InCVSReadOnly
Ignored
Added
Deleted
Locked
That is nine different icons - many more than this are not practical, since Explorer has a hard limit of fifteen icons in total.