HTML in User Signature

I am trying to add some html to my signature as admin

My code is as follows

<script type="text/javascript">

var code =new Date(2016, 0, 2)

today=new Date()

var one_day=1000*60*60*24

 document.write(Math.ceil((today.getTime()-code.getTime())/(one_day))+

" increase number equals")

</script>

The days increase as they should but the page does not return to the thread, it just gives me a blank page with the script results on them - Is there something wrong with my code or is it that the board does not like it?

Thanks