CodeTwo Exchange Rules lets you have different signatures/disclaimers for messages sent by users from different Active Directory groups. You need to configure separate rules for Active Directory groups that will have various disclaimer text.

1. In the main screen of the program, click Add in the toolbar to start creating a new rule.
2. In the Senders' scope, specify the Active Directory group the rule will apply to (Fig.1.).
3. Configure the rest of the settings according to your needs. Short guide to creating a new rule in CodeTwo Exchange Rules is here, in CodeTwo Exchange Rules 2007 and 2010 is here.
4. Compose the signature for the group using the built-in signature editor (as described here).
5. Save the changes in the program's main screen.
6. Set the rules for the remaining groups in a similar way.

Fig.1. Specifying the scope of senders as the Active Directory group.

See also:

How to insert an image into a footer

How to have parts of disclaimers/signatures removed on the fly when they have not been replaced by data from Active Directory