Just FYI, Signal (Open Whisper Systems) is not FOSS-friendly. The server-side software is not open source, they refuse to federate with other Signal implementations, and they are unfriendly to forks. See:
I recommend using Molly instead if you need to communicate with Signal users. Note, the Molly-FOSS flavor excludes proprietary Google libraries entirely.
If you are interested in trying an alternative that is unrelated to Signal, I suggest looking at SimpleX Chat.