When the current document is not saved or is out-of-site, this logo is not enable.
The current document and included files are targeting for Backup.
You can backup the files with orignal file together.
Ex. hoge.jpeg is backuped with hoge.png
"label" is writed out to ".label.txt" and the function of "Restore" is testing now.
The files for Backup are selected in the Site Panel.
The Folder for Backup is selected in the Site Panel.
The Folder for Backup is open with Finder(Mac)/Explorer(Win).
UI: Right-click on the Files Panel -> choose "Backup selected files..."