This is the validation result if you sign a file and after that change its content:

I think the wording could be improved. We should at least add some more information, as IMHO for a user the combination of "The signature is VS-NfD compliant" and "The signature is invalid: Invalid Signature" is contradictory. As well as linguistically ugly with the doubling of "invalid".

How about something like "The signature is invalid for file <abc.txt>" instead of "The signature is invalid: Invalid Signature"?
And possibly to be more verbose: "The file has been changed after the signature or the wrong file was given for verification."

And if there are other possible reasons for an invalid signature, I would like to have them listed here in some form, too.