When Google searching, most results for the Outlook 2003 Signature Folder Location AppData give you the wrong folder.
They mix environment keys like UserName, UserProfile, but should use AppData as that has been the base since at least Windows XP.
This is the correct folder for any Outlook version (2003, 2010, etc): %appdata%\Microsoft\Signatures
Making sure you use the right environment variable is very important, especially in large Windows based environments that often use roaming profiles and a mix of Windows environments.
For instance, at a client they have a mixed environment of Windows XP and Windows 7, with separate AppData locations for the two on a LAN:
- Windows XP:
- Windows 7:
There is a very nice Wikipedia article on the Windows Environment variable that explains this situation in the synopsis.