I am talking about these circle thingies: https://i.imgur.com/2lyMez5.png
There is no indication that they can be clicked (until you mouse-over them), no indication as to what they do when you click them. I had no idea I could mark specific notifications as read/unread until I tested what clicking the little circle does, I thought it was only an indicator to make it more clear which messages were unread. I know some other users would be wary of "clicking things to test what they do".
I suggest a button-looking button that looks like this: https://i.imgur.com/XVMBax7.png