In order to check whether an app has a valid signature and is notarized, use the terminal command below:

$ spctl --assess --verbose {PATH_TO_APP}

or

$ spctl -a -v {PATH_TO_APP}

App without notarization:


App with notarization:


If the signature is valid, the first line should show the output "accepted" next to the app name. The second line shows type of certificate (E.G. Developer ID) that will be prefixed with "Notarized" if the app was successfully notarized.