WebRTC is encrypted by default, using TLS for wss signaling and DTLS (TLS on UDP) for SRTP encryption. See the section Encryption Everywhere of WebRTC Chapter.
Encryption of media and data streams is mandatory. Full stop. There is no way you can have a WebRTC communication without encrypting the streams that are exchanged. Those would be the media streams (audio+video) and, if present, the data streams. Media streams are encrypted as SRTP with key exchange via DTLS.
Session protocol's signaling (SIP or VERTO) is encrypted too. The transport of choice for such signaling is usually Secure WebSocket. You will see almost everywhere the URI prefix WSS:// (WebSocket Secure) when defining WebRTC signaling servers and endpoints. WSS signaling exchange is encrypted by TLS.
