maybe open with what this is, first time I heard of it. to anyone similarly clueless, that's a proxy for other people to use that can't get at Signal's servers because it's blocked in their country or sumsuch.
in nginx you set up a proxy, like mysignalproxy.net:80 gets proxy_pass to your internal network's 172.16.12.34:980 and the same for 443
the simplest config is thus:
server {
listen 80 http;
server_name mysignalproxy.net;
proxy_pass http://172.16.12.34:980/;
proxy_pass_request_headers on;
proxy_set_header Host $host;
etc