Is this Norton 360's backup marker?
Have a look at your Norton 360 Help files.
This is what it says:
Backup Status Overlays
Lets you view the backup status of a file by adding the status overlay to the file's icon
The status overlays that appears are:
Green icon with a check mark
Indicates that the file has been backed up
This icon changes to blue icon with arrows if you modify the file etc.
Also look at this post
The page was slow to open, so be patient.
I presume you have tested the files to see that they open normally with Word.