Valid, unverified/verified signatures

[Lars Noodén]

I have a question about the verification of signatures made by SSH keys. 
  I've pored over the manual page for ssh-keygen(1) but not seen (or 
have missed) the relevant information.  The search engines have not 
turned up anything about that use-case either.

The context is that when using SSH keys to sign files using 
ssh-keygen(1) there seems to be a flag which shows if a signature is 
verified or unverified.  Viewing a verification while using increased 
verbosity shows a unverified status for the key being used:

  "debug1: Valid (unverified) signature from key SHA256:..."

I presume that a corresponding verified status is possible.  What should 
I be looking at to make the signature verified?

/Lars