Check if person "Likes" the facebook page.

facebook-like-check.php

<?php
/*
 *  Check to see if a person likes the current facebook page.
 */
 
$signed_request = $_REQUEST["signed_request"];
list($encoded_sig, $payload) = explode('.', $signed_request, 2);
$data = json_decode(base64_decode(strtr($payload, '-_', '+/')), true);

if (empty($data["page"]["liked"])) {
	echo "You are not a fan!";
} else {
	echo "Welcome back fan!";
}
?>