After you subscribe to iTunes Match, you may notice new cloud icons appearing in your iTunes music library on your computer. Here’s a quick explanation of what the new icons mean.
This icon is displayed when a song has been removed from iCloud (from a different computer). Songs deleted from iCloud are immediately deleted from associated iOS devices, but will remain on other associated computers until they are manually deleted.
This icon may be displayed if the song file is corrupt or if there was an error uploading the song. Try updating iTunes Match (Store > Update iTunes Match) to resolve this. If updating does not resolve the issue, try importing a new copy of the song into your iTunes library.