Thinking further, maybe the participant block could indicate that, or what is the user using at the time.
Does anybody know of any add-on that indicates when somebody is using the chat. I sometimes go on-line at time that are not scheduled, and would like my student to know that I’m using the chat (or anybody else). It would be nice to have a block that indicates who is active in a chat.
This doesn't exist in Moodle at present, but it's something that the COVCELL project are working on. Search for COVCELL if you want to know more about that...