How to publish artifacts signatures (.asc files) using maven-publish plugin?

Obscure?
Imho it is pretty good documentation, especially compared to other software documentations.
It is clear, concise, has good examples.
The page I linked you to already (https://docs.gradle.org/current/userguide/publishing_maven.html) even has a complete self-contained example of a build script that builds a library and publishes it including a javadoc artifact and a sources artifact and all signed.