Tuple has a mode where instead of drawing, you can click to show a kind of (as I remember it) radar indicator of where you clicked. It's a nice way of pointing stuff out as a guest without the effort (I'm lazy) of drawing a line or circle.
Instead of adding another mode, maybe just clicking in drawing mode, without dragging the mouse, could show some sort of stronger indicator around the spot you clicked. Or if you think it would be confusing not to be able to draw a small dot, maybe holding down for some number of milliseconds without moving the cursor could achieve the same.