The signal is built to never acquire or retain any personal information. They or other third parties can not access signal messages and calls as they're often encrypted, private, and secure end-to-end.
State-of-the-art end-to-end encryption (powered by the Signal Protocol for open source) keeps your communications secure. The signal app is unable to read your messages or listen to your calls, and neither will anyone else.
Privacy is not an optional mode, it's just how Signal runs. Each message, each call, every time.