In addition to your Peerio Public Key, Peerio also assigns you a cryptographically generated avatar that can be used to verify your own or your contact's identity. You will find a user's avatar in your contacts page next to your contacts names. It will be an image with four small digital characters.
As an alternative to exchanging public keys with a contact, you can describe your avatar, e.g.
Although it is very unlikely, if you notice someone's avatar change, their account may have been compromised. Peerio will notify you if this happens, and it is advised to communicate with your contact outside of Peerio to confirm that you both are seeing the same avatar.