Regarding if the sign of the Zeta is a triangle. It is not. Where Whitely Strieber is telling a true story, and relaying faithfully the occurrence, the entities visiting him and the orientation of the entities are not clarified by the author. Like many in today's time, Whitely was confused as to what the entities were after, and whereof they spoke. And like many contactees today, Whitely was visited by entities from both orientations. He failed to differentiate. All frightened him, and the insignia from one was assigned as the insignia of all. We, the Service-to-Others Zetas, have no such insignia. In fact, we have no insignia at all, as much as this will be disbelieved by many. As we are Service-to-Other Zetas, we are highly telepathic, and are known to each other without the need of insignia.
The triangle belongs to another alien group, of the Service-to-Self orientation. Insignias are required in these groups because they are not given to telepathic conversations, being distracted from the primary goal, the self, with such matters, and require insignias in order to identify their various groups.