Comment by monocasa

If I was the NSA, I would be using the fact that signal uses AWS for their backend combined with the cudgel that .us.gov has with the AWS govcloud contract to mandate that all traffic to and from signal's backend also gets routed to NSA traffic analysis servers, which could then be correlated with other sources like ISP data to get a pretty complete record of all Signal message metadata.

To be clear, I use signal pretty heavily, but that's because my threat model doesn't really include competent .us.gov actors. I don't think that they'd either prove they're doing this or go through the trouble of parallel construction over anything in my messages or who I'm talking to.