;;

These could be representing a sweat drop (or two), which are commonly found on the faces of many anime characters. It's generally used when the conversation is awkward or embarrassing.

Bryce: Have you read that book I borrowed you yet?
Selena: No. I haven't had time to...
Bryce: Oh.
Selena: Yeah... ;;
--

Crystal: There's this test I'm supposed to take today, and I haven't studied at all. I am so fucked. ;;
Terra: You could always cheat?