Check if ignore cookie exists

Hi!

I am thinking of displaying a small padlock icon in the footer of my website when user has opted-out from Piwik statistics on my site.

I think this code should work:

<script type="text/javascript">
if (document.cookie.indexOf('piwik_ignore') != -1)
document.write('cookie is here');
else
document.write('cookie is not here');
</script>

The problem is that I am not sure how the ignore cookie is called. I thought it was piwik_ignore but it does not seem to work.

Any ideas? Is it even possible?