How to Turn on Registration Lock in Signal Feb 17, 2021, 9:30 am EDT | 2 min read Signal, the secure messaging application, ties itself to your phone number. For extra protection against thieves stealing your phone number, you can enable Registration Lock, preventing anyone from registering another account with your phone number. What Is Registration Lock? Your Signal account is tied to your phone number, which means you don’t even need a password to log in. Your Signal account can only be linked to one phone number, so you can only have Signal active on one iPhone or Android smartphone at a time.