I have followed the instructions from: http://maven.apache.org/guides/mini/guide-central-repository-upload.html
These make no mention of needing to sign the artifacts. The link you provided is for Maven developers, isn't it? I have other projects being rsync'd and this is not needed either. I suppose this is a new effort for security...
Since I have already released the artifacts, is there a way to sign the existing ones already in the repo?