Signal secure messaging app stops working in China The app has been one of the last US social media platforms that isn't blocked by Chinese censors. Signal has recently seen a surge in users, with over 500,000 downloads in China. Users of Signal discovered they were unable to access the app without a VPN Signal's website has been blocked since at least March 15, according to the GreatFire.org website that tracks online censorship in China. However, the app remains available on app stores in China. The iOS version, which works with Apple technology, had been installed close to 510,000 times to date in China, said research firm Sensor Tower. Android data for the app is unavailable in China.