Image Manifest V 2, Schema 2 does not contain signature metadata

Whilst looking at how to use asymmetric keys to sign and verify the mainfest file I found the Image Manifest V2, Schema 1, which contains a signature section, once checked provides assurance that the layer SHA hashes are correct.

Is Schema 2 lacking documentation in this feature or is it intentionally removed?

What is the current recommended way for me to insert a signature into a manifest file which can be stored in a registry. Ideally I would like to contain my signature in the manifest file so that I do not have to have a separate server to maintain a list of hashes / signatures

Thanks!