Signature files for Outlook 2003 reside in the %appdata%\Microsoft\Signatures folder. There are three ways to make Outlook to use a particular signature with all accounts:
1) Apply the hotfix described in MSKB article 898076 and then set the NewSignature and ReplySignature string values in the HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\11.0\Common\MailSettings key to the name of the signature. This applies the signature as a policy. (Of course, the user can still delete it from the message itself.)
2) Same as #1, only set the NewSignature and ReplySignature string values in the HKEY_CURRENT_USER\Software\Microsoft\Office\11.0\Common\MailSettings key.
3) Use a script like that at
http://www.outlookcode.com/codedetail.aspx?id=821 to apply the signature to each account.
If you want a true mandatory signature that the user cannot delete, you need to apply it at the server, as described on the page you cited.
