content: From what I understand, Signal uses Google's GCM to relay messages and get the status of the message (whether it was received by the device or pending delivery). Assuming the app actually encrypts the messages before it leaves the context of the app, I'm not sure what the real problem would be. Google can intercept the message just like any other network provider. Also keep in mind you're typing the message on an Android device anyway. You pretty much have to trust someone else's code or infrastructure at some point. That's why end-to-end crypto is important.