Considering Signal has been subpoenaed several times and proven in court the only thing they can give the feds is:

1. Do you have an account with Signal? (Registered Phone #)
2. When did you make the account?
3. When did you last connect to the service?

I don't think it'd be in their best interest to lie to the feds 6 times. You can quite literally read the subpoena for yourself, such as the most recent one in August 2024, which is only 2 pages long.