Found a solution…
Used: User Config -> Preferences -> Windows Settings -> Files
To ‘replace’ the files in the ‘Signatures’ directory.
The loaded the Outlook 2003 ADM template (from Office 2003 ORK).
Used a custom AD template ( http://www.office-outlook.com/outlook-forum/index.php/m/185258/ ), which adds 2 options, to specify which signature to use for “New” and “Replies”.
It adds the options under : User Config -> Admin Templates -> Classic Admin Templates -> Microsoft Office Outlook 2003 -> Tools | Options.. -> Mail Format -> Signature
Now whenever I update the ‘master’ copy on the network, it gets copied to staff PCs, and then defaulted (and they’re unable to edit).
Just what I was after 🙂