Mail.app: How can Choose Signature choice be based on recipient? I have different mail signatures that I'd like to use, depending on whether my recipient is internal or external.  In the Signatures tab of Mail.app preferences, I can choose random or sequential only.

Has anyone set this up?  Anyone have any pointers on how to get started on something like this?  Even being able to choose signatures via keyboard shortcut would be an improvement.
I have heard on different podcasts of users who use TextExpander to shortcut into typing different e-mail signatures. 

TextExpander is on my wish list of apps I will buy soon, I see a lot of potential in having keyboard shortcuts for common text snippets. Hope this helps.