You can inspect the response header and get the information of the server.
Server:nginx/1.10.1 + Phusion Passenger 5.0.30 X-Powered-By:Phusion Passenger 5.0.30
To hide this information, edit your nginx.conf, add these lines in http block.
server_tokens off; more_set_headers "Server: CalvinMy"; more_clear_headers X-Powered-By;
In your passenger.conf, add these lines.
Finally, restart your nginx server. Now you will see "Server: CalvinMy" in the header and the "X-Powered-By" header is removed.