Signal is end-to-end encrypted. The only thing the network surveillance would be able to determine is that you were connecting to Signal via an open Signal proxy, not the people you were talking to, or the content of your messages.
When proxying, who you're talking to can be determined from large-scale network surveillance. You look for patterns of messages sent from your device and messages of the same size received by another device immediately after.
Yes? To some people just that fact would be revealing of needing to use Signal, it could be used in prosecution. Especially in the case where most people would not be using it at the moment.
Revealing the fact that one uses Signal can be an issue on itself.
