Er...actually, that's not true. The display of the tray icon depends solely on whether it's turned on in the registry, which is controlled by the System Center. You can doublecheck on the clients by looking in HKEY_LOCAL_MACHINE\SOFTWARE\INTEL\LANDesk\VirusProtect6\CurrentVersion\AdministratorOnly\General\ShowVPIcon to see if it's set to 1 or 0, although if you change it it will be overwritten the next time the client checks in with the server.
You can also check to see if Vptray.exe is in the Run key, since that's where it starts.
Hanlon's Razor: Never attribute to malice that which is adequately explained by stupidity.