Chat indicators are the small attention markers that show up in the right upper corner of the chat to let the agent know something happened to the chat. There are a few indicators available - once a new chat comes in; when the agent hasn't replied within 60 seconds; when the customer hasn't replied within 2 minutes; when the visitor left the website; when the visitor closed the chat etc. They all have different colors and different icons inside, to be easily recognized.
This is an example of the "New Chat" indicator - it is on the right upper corner of the chat, it is in red and there is a small number inside, showing the number of messages the customer has sent.