I hate the term, but starting in 2013 I decided to be more proactive about the emails I receive. With regards to newsletters, unless it provides information not available elsewhere through RSS, Twitter or the like, I unsubscribe. Synergising my inbox paradigms.
Having clicked the unsubscribe link in a StackExchange email, I was presented with the above image, and a comment.
We couldn't find the page you requested, but we did find this sign that might help.
While technically true, I doubt sicking a panda onto my inbox will rid me of your newsletters. That is, unless it somehow overcomes its bamboo addiction and begins ingesting them on my bearhalf.
Jokes aside, having unsubscribed to dozens of newsletters so far this year, errors like this are disturbingly common, regardless of the browser or platform I use. I suppose some sites figure if they make it non-trivial to unsubscrube, you'll just stick with them.