I just got prompted by captcha to enter in the pi symbol. Not really possible on any keyboard I've seen. Could be an issue with the new site.
I'd recommend reading up on reCAPTCHA.
TLDR: reCAPTCHA is a system that uses captcha strings to parse books that its OCR can't read. You are presented with 2 words- one is a control word that reCAPTCHA knows- the other is a word is hasn't yet determined to sufficient accuracy. So, if you get one word you can read and one you can't, just take your best stab at typing the unreadable one, since it's probably not the control word.