No. None of your network traffic is private and you can assume it's being read.

https://en.wikipedia.org/wiki/33_Thomas_Street#Usage

https://theintercept.com/2016/11/16/the-nsas-spy-hub-in-new-york-hidden-in-plain-sight/

https://theintercept.com/2018/06/25/att-internet-nsa-spy-hubs/

https://www.propublica.org/article/a-trail-of-evidence-leading-to-atts-partnership-with-the-nsa

Things like HTTPS (web traffic) are backed by certificate authorities which could be compromised. Your cellular radio traffic is encrypted, with keys controlled by the phone company which has the same problem. It's been shown in several cases (like the Snowden leaks) that ISPs and tech companies cooperate with the NSA.

That being said, well implemented encryption using sufficiently large keys allows you to communicate over networks even if they are compromised. All of this is only secure as the endpoints. All of the encryption in world doesn't help you if an adversary has root access to a device in the conversation.

I can't tell you that you should trust Signal, I'm just a screenname on the Internet. However, if you look at the people who have the authority to directly ask intelligence services about their collection capabilities... those people use Signal.