For the immediate issue, using squares instead of circles for corner points would seem to read really nicely; possibly, going with what Illustrator does (IIRC), filled circles instead of hollow circles could mark end points. I'm not sure about tangency, etc.; I'd generally be inclined to use a text label that appears on hover or when the point is visible, instead of trying to find an unlimited number of different symbols -- that seems likely to be more legible. The basic few cases, though, could definitely use more distinction. A list of checkboxes could handle the UI just fine, similar to how object snaps are handled now, although probably living in the view pane of the options menu. "Show corner points as squares", "Show end points as filled circles", "Label other point types".