If you're using Outlook 2003 the Signature settings under the Tools menu.  Click Tools->Options and you'll get a popup window with some tabs in it. 



Switch to the Mail Format tab and under "Signature for new messages" and "Signature for replies and forwards" find the signature labeled for your restaurant and select it.  If you want to customize the signature and put your name or contact information above the banner, you can click on the "Signatures" button

You'll get a window that looks a lot like this:


Find the signature for your restaurant and click on edit.  Edit it to add your personal information and click OK to save it.

That's it!