I have had it installed for a week but uninstalled immediately when I got a push notification that another contact also had signal.Just because we both use signal doesn't mean I want to be reminded of them.And that made me think, if I was reminded of them, then it works the other way too. Literally anyone in my hundreds of contacts could be getting notifications that I am on signal, do they want to connect with me? Do I want them to also know I am on signal?A lot of my contacts are ex clients, networking flybys, even random people I shared numbers with drunk at a club. Many are professional contacts, others I just want to monitor if they ever try and contact me, maybe one day I want to talk to them, on my own terms.By consenting to give signal access to my contact list I didn't want to opt in to giving them carte blanche to broadcast my presence to every random person I have ever sent a message to. But that is not an option when setting it up, 
and that is what it will do.I have 20 years of contacts, and I don't want many of them getting any kind of notifications with my name in it. I don't even have anything interesting to hide. But if I decide to re enter a person's life I want to do so on my terms and not that of an algorithm.So I uninstalled. Then I reinstalled and did not grant permissions to access my contacts.Lo and behold after reinstalling without contact list permissions it knows the names of people in my contact list if I manually enter the mobile number. On the second install, these details must be getting fetched from the server, assuming android permissions are solid, because I provided my contact list in the first place.I checked with a friend who also reinstalled and he is seeing in signal the full name of a person he hasn't contacted through signal, by their phone number. Which must be due to sharing the contacts the first install.Lesson learned not to share contacts with any app ever.Signal is not a panacea is all I can say.