From the Wiki I linked in my post just before yours:
18. Where are the WD desktop and tray icons?
Windows Defender can be found on the Start screen, All Apps. If you really want a Desktop icon, do the following:
Use the charms, and search for Defender. Alternatively, go to the Start Screen, right-click, and select All Apps. Under the Windows System group, you will find Windows Defender.
Once you have found Windows Defender, right-click on it and select Open File Location. There you will find a shortcut to Windows Defender. Copy the shortcut, and paste it on your Desktop.
There is no tray icon with WD on W8. The Action Center icon reports WD issues.