Outlook roaming signature vs Signatures on this device

I've been able to set default signatures using registry keys as long as the signature is associated with the user's account. This produces the desired default sig you set, but the setting in the Outlook signature settings screen doesn't appear any different. If you check the signature files generated in AppData\Roaming\Microsoft\signatures the ones associated with the account are appended with the user's email in brackets. Just adding this to the signature file name seems to do the trick so that it then appears in the Outlook account signature list rather than the local device one.

To associate signature with account: 

Change the signature file name in your script to "[SignatureName] ([User Principal Name]).htm" e.g. "Maddiebean's signature (email address removed for privacy reasons).htm" and it should appear in the user's email dropdown rather than 'Signatures on this device'. Worth noting the UPN is case sensitive in the filename too.