Signal is among my most favorite of apps with strong privacy protections. Signal has now been around for a decade, and media outlets are featuring articles about it. I cannot imagine a better person being Signal's president than Meredith Whittaker. She has the smarts and the courage to make Signal be all it can be. She is an interesting person too, on her own merits.
Brew up some good coffee and have a read of Whittaker's interview in Wired. Beware of the pretenders out there who will collect information on you and sell it, or would allow it to be used to block your access to info or interactions you seek. For more on that, see Surveillance Watch, which Whittaker has cited as a great resource, covering the connections between surveillance companies, their funding, and their unsavory clients.