Using the X-Robots-Tag HTTP header
The X-Robots-Tag can be used as an element of the HTTP header response for a given URL. Any directive that can be used in an robots meta tag can also be specified as an X-Robots-Tag. Here's an example of an HTTP response with an X-Robots-Tag instructing crawlers not to index a page:
HTTP/1.1 200 OK
Date: Tue, 25 May 2010 21:42:43 GMT
(…)
X-Robots-Tag: noindex
(…)
Read more here:
https://developers.google.com/search...obots_meta_tag