jQuery - Text toggles only once

I have a simple script that should change from + to - when the Content is open, and backwards.
But now, when it changes to -, it stays as - no matter what. Even if you collapse the content, it still stays as -.

I've tried to reverse the functions, but it just did the same with the +.

jQuery

$(document).ready(function(){
    $("#expanderHead").click(function(){
        $("#expanderContent").slideToggle();
    if ($("#expanderSign").text() != "+"){
        $("#expanderSign").html("-")
    } else {
        $("#expanderSign").html("+")
    }
    });
});

HTML

<span id="expanderHead" style="cursor:pointer;">
    Lorem ipsum Lorem ipsum Lorem ipsum.
    <span id="expanderSign">+
    </span></span>
    <div id="expanderContent" style="display:none; color: green;">
    <sup><p>Lorem ipsumLorem ipsumLorem ipsum<br>
    Lorem ipsumLorem ipsumLorem ipsumLorem ipsum,<br>
     Lorem ipsumLorem ipsumLorem ipsum.</p>
     </sup>
  </div>