No error message on signature failure due to missing Referer header

[hdastwb]

I tried signing a couple of petitions on https://petitions.whitehouse.gov, and whenever I clicked the "Sign Now" button I saw the spinner appear for a moment below it but didn't get any other indication of whether the request had succeeded or failed. I did some more investigation and noticed that the problem went away (my signatures went through) after I temporarily re-enabled the Referer header (I usually browse with that off), and so the problem seems to be caused by the site rejecting AJAX requests without Referer headers (though I wouldn't be surprised if there are a few other conditions that will lead to the same behavior). The site should show some kind of error message when requests fail for reasons like this so that users can tell that they've failed.