<style type="text/css">
.spoiler {
background-color :#ffffff;

background-repeat: repeat-x;
}
.spoilerheader {
padding-left : 15px;
background-image : url(http://school136.org.ua/img/favicons/plus.png);
background-repeat: no-repeat;
background-position:0 1;
display:block;
}
.spoiler.open .spoilerheader {background-image : url(http://school136.org.ua/img/favicons/minus.png);}
.spoiler .spoilertext {display:none;}
.spoiler.open .spoilertext {display:block;}
</style><script language="javascript">
function spoiler_on()
{
//document.getElementById('spoiler').style.visibility='visible';
document.getElementById('spoiler').style.display='';
}
function spoiler_off()
{
//document.getElementById('spoiler').style.visibility='hidden';
document.getElementById('spoiler').style.display='none';
}
</script>

в вид материалов форума находим

Code
$SIGNATURE$

Меняем на:

Code
<div class="spoiler"><a class="spoilerheader" onclick="this.parentNode.className=this.parentNode.className=='spoiler'?'spoiler open':'spoiler'">Подпись скрыта</a>
<div class="spoilertext">$SIGNATURE$</div></div>