Troubleshooting Step 1:

Check if the file/folder is actually encrypted by doing the following:

1. Right click on the folder in Windows File Explorer and click on Properties.
2. In the Properties window, if a tab named Symantec File Share is present, the folder is encrypted:

Right click on PGP Tray from the notifications area of the taskbar and choose Options or open Encryption Desktop and choose Tools / Options from the menu. Check in the File Share tab that the Overlay PGP icon on secured files and folders option is enabled:

From Windows File Explorer, navigate in and out of the protected folder or simply try waiting a few minutes.

Ensure that you are running the latest version of Symantec File Share Encryption.

Troubleshooting Step 2:

The other method is to do a "--list" command on the share via the command line with pgpnetshare.exe:

pgpnetshare.exe --list "folder path here"

This will show you all the users and roles, so you can use the pgpnetshare.exe binary to check on all of these attributes.

When the shares themselves are massive, it does take Windows time to render the overlay icon.

Also, the icon size can also affect if this is showing up or not...if you change to "Details" or tinker a little bit with the sizing of the folders:

Troubleshooting Step 3:

If there is other software that has its own overlay icon, it may have priority and cause the File Share Encryption overlay icon to not appear.

Troubleshooting Step 4:

It may also take some time to refresh the overlay icon on very large shares that are encrypted. 
Sometimes waiting is all it takes, but is more effective to check the properties tab.