To finish signing up to a Socrata site, you need to complete a reCAPTCHA challenge.
If you find the challenge to be mostly unintelligible, the feature should have a 'refresh' option right next to the field where you type in the characters, which when clicked on will prompt a new challenge to be displayed. It should look like an icon with circular arrows.
There is no limit to the number of time you can refresh the challenges and they generally get easier the more your refresh.
Note: if you sign up for a Socrata account and receive a Site Unavailable error, it is likely due to an incorrect CAPTCHA phrase.