Signal is a centralized service where:

- You have to trust their servers to run the code they tell you is published on github.

- You give your phone number to create an account and they look for contacts, aliases do not allow you to create an anonymous account.

- The metadata is not private.

- Easily censored by an ISP.

- Its desktop versions are based on chrome and do not encrypt the information, which makes it trivial to extract.