I'm in the process of creating a Facebook app that uses a Page Tab. However, when I access a page where the app is installed a signed_request parameter is not sent to my script. Neither $_POST nor $_REQUEST are being sent any data (and using the Facebook PHP SDK $facebook->getSignedRequest() also does not work)
It turned out to be a stupid oversight on my end, I had typed http://example.com which redirected to http://www.example.com the redirected page didn't have data posted to it.