Add a mark about saved document would be good thing.
Drawing/painting process consists not only from moving stylus around tablet. A lot of thinking, searching on the web and making a coup of tea is part of it. And save action is part of whole process like a stairstep, post or support. And each next step is sort of experiment. So it is good to know where this stairstep was, and to which I can jump back or retreat.
So the mark can be in text form like “Brush stroke (saved)” or changing color or add small mark near action. Actually anything that differs flow in a history dock should be ok.