Question

What sign does Zeus send as an omen?

Answer 1

In the story the odyssey if that's what you are talking about then the sign was the two eagles dropping down on the congregation(group of people) fighting with their sharp talons ripping each other apart and its impending doom for them.
(delete the comment below your question i put it there because i thought i wasn't going to be able to comment the answer because 2 people were answering)