include 'html/sign.htm';
$_GET['signsubmit'] = $submit;
if($submit == 'true'){
die();
}

<form name="login" id="signform" method="post" action="sign.php?signsubmit=true">
................
<div class="center"><div class="button"><input class="button" type="submit" name="signsubmit" value="註冊並登入"></div></div>
</form>

die("呢度要打字")

$submit = $_GET['signsubmit'];

$_GET['signsubmit'] = $submit;

$submit = $_GET['signsubmit'];
if($submit == true){
die();
}

<?php
$submit = $_GET['signsubmit'];
if($submit == true){
die();
}
?>
<form name="login" id="signform" method="post" action="a.php?signsubmit=true">
<div class="center"><div class="button"><input class="button" type="submit" name="signsubmit" value="註冊並登入"></div></div>
</form>

if(isset($_GET['signsubmit'])){
die();
}

<form name="login" id="signform" method="post" action="sign.php?signsubmit=true">
................
<div class="center"><div class="button"><input class="button" type="submit" name="signsubmit" value="註冊並登入"></div></div>
</form>

<?php
$submit = $_GET['signsubmit'];
if($submit == 'true'){
die();
}
?>
<form name="login" id="signform" method="post" action="a.php?signsubmit=true">
<div class="center"><div class="button"><input class="button" type="submit" name="signsubmit" value="註冊並登入"></div></div>
</form>