What do the icons mean in the photo view? It seems to be in any view of a directory or multiple photos.

I see:

• R's (meaning I have reviewed an image in this software?)
• little disk like things with a line and little yellow dot in the center underneath (meaning the photos in in the database?),
• Little pencils or tags (meaning the photos has been modified from its original?)
• Little balloon shaped icons (GPS information available)

Those are just my best guesses at what the icons mean- it would be helpful to understand this and what other icons/symbols are available. I could not find this in searching the help and documentation index.