Two or more points are vertical if they lie on an imaginary line that is parallel to the y-axis. There is no indicator for a vertical points relation.
To detect a vertical points relation implicitly
The points are snapped as vertical.
note: A vertical points relation can be detected if the Vertical Points check box in the Tools | Options | Relations tab is selected.
To detect vertical points relation through snapping
Use the vertical points snapping mode to detect a vertical points relation for the control points of the object you are currently drawing and thus snap the point accordingly.
Example
The example below shows vertical points:
note: Since a vertical points relation is defined between a line or two points and the y-axis, when you move vertical points they are not kept parallel to the y-axis: a vertical points relation is detected, but is never set.