Unless disabled both nginx and PHP give away their version in the HTTP Header. Here is what that looks like:
$ curl -I http://test.local
HTTP/1.1 200 OK
Date: Fri, 11 Apr 2014 08:20:36 GMT
Content-Type: text/html; charset=UTF-8
Vary: Accept-Encoding ...
2016-05-25 265℃ 0 COMMENT