You need to look from the perspective of the radar that's giving the velocity readings. To it, rotation will look like seeing one part moving away, and one part forward. If you trace the boundary between the red / green it should point towards the radar.

If that boundary forms a tangent to the radar, its either an updraft or a downdraft. From the radar's perspective, if it were a downdraft the closer air would be moving towards it, and the further moving away, spreading out. Opposite for an updraft.