If you consistently watch the same streamer, an icon will be displayed after your username according to your watch streak. Your watch streak number will be displayed when you join their stream.
If you do not go to watch their stream even once, your watch streak will reset to zero.
*If the streamer you are on a watch streak for streams for less than 30 minutes, and you do not view that stream, your watch streak will not reset to zero. Additionally, if you view a stream that ends up being less than 30 minutes long, your watch streak will count for that day.