Particularly interesting given that some of these problems were pointed out to Docker folks ~4 months ago in the development of the feature.
https://github.com/docker/docker/issues/8093#issuecomment-57...
Clearly nobody changed anything in the docs to clarify. Like most things security related people don't care until there is a major exploit or somebody with enough clout complains enough, or more likely than not both.
[1]: https://github.com/docker/docker/issues/8093#issuecomment-65...
I don't think there's anything yet in the docs with regard to signed image, apart for the release notes[1] mentioning it being a "sneak peak" of a coming feature, that is under development
[1]: https://docs.docker.com/v1.3/release-notes/#new-features