I _think_ (correct me) you might think of the Android app's dependency on the proprietary Google services. As far as I'm aware, Signal doesn't run without GApp

I _think_ (correct me) you might think of the Android app's dependency on the proprietary Google services. As far as I'm aware, Signal doesn't run without GApps on Android by default, exactly because of the GCM dependency (but you seem to be able to dodge that with the help of the microG project).