function isSerialized($value) {
	$unserialized = unserialize($value);
	if ( $unserialized !== false ) return $unserialized;
	if ( $value != 'b:0;' ) return false;
	return $unserialized;
}

/* oder als Alternative */

function isSerialized($value) {
	$unserialized = unserialize($value);
	if ( $unserialized !== false ) return true;
	if ( $value != 'b:0;' ) return false;
	return true;
}