A task to have standard Outlook signatures started me on a Google search.  I found solutions for setting up the signature on each user’s computer for small companies as well as some applications for sale that would allow you to tweak Outlook for larger companies.  What I ended up doing was taking a snapshot of a VM machine before and after I applied the signature.  I then used WinInstall LE to find what changes occurred to the system between the before and after snapshot.  The actual signature is saved in three formats (html, rich text, and plain text) in %UserProfile%\Application Data\Microsoft\Signatures.  A personal profile configuration file (*.pip) is also changed in Outlook called MSOut11.pip.  This file is located at %UserProfile%\Application Data\Microsoft\Office.  By modifying the three signature files for each user, and adding these files to the user’s profile, you can create a standard signature for anyone in a company. 

Disclaimer: This currently has only been tested in a terminal server environment running Windows Server 2003 and Microsoft Office 2003.