Developer on appear.in here: Everything between peers is encrypted using SRTP end-to-end by default. From our FAQ:

"All communication between your browser and appear.in is transmitted over an encrypted connection (SSL). Video and audio transmitted in the service is sent directly between the participants in a room and is encrypted (SRTP) with client generated encryption keys. In some cases, due to NAT/firewall restrictions, the encrypted data content will be relayed through our server."