My identicon (the automatically generated pattern next to my username) is the same for all of the Stack Exchange sites I use. I was confused to see a different shape and colour identicon next to my username when I signed up for Area 51. Since the pattern is based on a hash of my email address (plus a salt), which is stored externally with gravatar, I don't understand how my single gravatar account could be providing two different identicons. Is this change of identicon part of the Area 51 theme or is this unique to me?
Typically, identicons are created based on a hash of your email address. But since you started using Area 51 as a non-registered user, the identicon was generated based on your last known IP address.
The identicon doesn't change automatically when you register, so I went into the "change your picture" function and simply re-selected the 'use identicon' function, and that seemed to take care of the problem. Everything seems to be in order now. Enjoy.