I tried Signal while Google Play Service was either uninstalled or disabled, Signal won't just work.
@EdwardTorvalds I'm using signal on e.foundation ROM (MicroG) all the time and it works perfectly.
This is largely a philosophical discussion - a patch that fakes a digital signature is certainly not something that looks good from security point of view, but that's only if you ignore the whole business context (=Google enforcing its monopoly with Google Services) and the patch has a very well-defined and limited scope.