There is nothing legally stopping people from forking the signal app and distributing it (even configured to talk to the official signal.org servers) so long as

There is nothing legally stopping people from forking the signal app and distributing it (even configured to talk to the official signal.org servers) so long as they don’t use the Signal trademarks. Also, as others pointed out, Moxie isn’t part of Signal any longer and hasn’t been for a while.