Ventu communication was accomplished via a sequence of gestures made with arms and hands. (VOY: "Natural Law")
The left arm was held out parallel to the ground, bent at the elbow so the forearm crossed the front of the body. The left hand was flat. The right arm was held in a similar position, but moved from right to left underneath the left arm. The right hand was in a half-fist with the fingers waving.
The right hand was held out in a cupped shape, and then quickly pulled up into a fist.
A fist was held out, and rotated while opening, to expose the flat palm of the hand facing upwards.