You may be receiving the following message when trying to sign up:
You must re-submit this request with a response to the captcha challenge
Captchas not displaying is known issue that we're working on fixing. Currently, this affects signups on the Disqus comment embed on websites.
How to workaround the issue
For the time being, we recommend you signup at https://disqus.com/profile/signup/ before going back to the site you wish to comment on.
We apologize for the inconvenience, and we're working getting this issue resolved soon.