Next I saved the following script as an application (with no startup screen) in my user's Library -> iTunes -> Scripts (I called it 'iTunes Not Work Safe').
tell application "iTunes"
set newcomment to (comment of current track) & " Not Work Safe"
set (comment of current track) to newcomment
end tell
Now if I run into a song that isn't work safe, I click on the script menu in iTunes, and select iTunes Not Work Safe, and that song will be removed from the smart playlist.

