HTTP 444 (No Response) instead of 404, 403 error pages?

Redirect request then you can return status code easily:

server {
  error_page 500 502 503 504 @blackhole;

  location @blackhole {
    return 444;
  }
}

Just wanted to add that using @blackhole named location raised Nginx's default 500 error page when certain weird requests were sent to the server (more details here), and thus the desired result (444) was not achieved.

I went around this by using the following notation instead:

error_page 301 400 403 404 500 502 503 504 =444 /444.html;
location = /444.html {
        return 444;
}

Update: note that if the above block is itself inside a location block, the location path location = /444.html {… may prompt an Nginx error upon reload because Nginx requires it be a sub-location of the parent location block --> such as: location = [sub-location]/444.html {….