Booking.com is recruiting, using HTTP headers.

$ curl -sI http://www.booking.com/index.en.html HTTP/1.1 200 OK Date: Sat, 14 Apr 2012 13:19:23 GMT Server: Apache X-Recruiting: Like HTTP headers? Come write ours: booking.com/jobs Vary: Accept-Encoding Content-Length: 170752 Content-Type: text/html; charset=UTF-8 Content-Language: en