How secure is Signal? It's good enough for Edward Snowden so good enough for you American whistleblower Edward Snowden in a tweet has vouched for the Signal app. He noted that Signal is secure and that he uses it every day. Yasmin Ahmed | January 10, 2021 | Updated 14:46 IST (Picture: Reuters) Highlights American whistleblower Edward Snowden has reiterated his faith in the Signal app by saying that he uses it every day. Snowden has been in favour of Signal app since its inception and tweeted that he used Signal back in 2015. Signal surpassed WhatsApp to become the number one app on App Store in the country. WhatsApp has kept February 8, 2021, deadline for users to accept the new terms of service.