Microsoft Outlook stores its files in obscure places. Make sure you are backing up your PST files by knowing the location for your version of Office and Microsoft OS or by moving the file to a known and simpler location. This is a work in progress, I’ll add as I find or need to know where Microsoft has decided to hide your files.
Windows Vista Outlook Signature Folder
%USERPROFILE%\AppData\Roaming\Microsoft\Signatures or %APPDATA%\Microsoft\Signatures
%USERPROFILE% is an environment variable (you can see what this is by opening a command prompt and typing “set” minus the quotation marks). Simply copy the above and paste into the Explorer address bar and it’ll open to that folder. In a few cases, if you’ve got a security freak sysadmin, it could be in a location other than the above.