So your question is really how to control what signature the user employs,
right? There are three ways to make Outlook to use a particular signature
with all accounts:
1) 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 stored in the
%appdata%\Microsoft\Signatures folder. This applies the signature as a
policy setting, so the user won't be able to change the automatic signature
(and may also be blocked from some other features on the Tools | Options |
Mail Format dialog).
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. This applies the setting as a user preference.
3) Use a script like that at
http://www.outlookcode.com/codedetail.aspx?id=821 to apply the signature to
each account. This is the brute force method, available if you can't apply
SP2 for some reason.
Note that even if you mandate a signature with a Group Policy Object, the
user can still delete the signature from the message itself, and the savvy
user can edit the .rtf, .htm, and .txt files for that signature. That's why
if you really want a mandatory signature, you must do it on the server; see
http://www.slipstick.com/addins/content_control.asp for links to tools.
GPO can also be used to set the Outlook editor as the only editor. Outlook
has no feature for limiting the number of characters in a message body.