We have launched a trial of shipping the official Signal releases in our F-Droid-compatible repository. We believe we can reliably ship them, using multiple layers of verification on top of the built-in APK signature Signal Foundation ships. This is the same setup that ships Tor Browser. We welcome feedback.
These are the same APKs that Signal Foundation makes available for direct download. They include the ability to self-update, so even if Signal is no longer included in our repo, it has a built-in update channel.