I think the failure of communication here is fundamentally one of concept. The intent of the design of Agon is that the PLAYERS interpret the signs, they're not something made up by the GM. Its not a puzzle to be solved! When you encounter an Agon Island you get 3 signs. Now, the GM/Island Author may have in their mind some kind of idea of what these signs might portend, but it isn't up to the GM to assign them meaning! The PLAYERS assign meaning to the portents and BY DOING THAT they establish what the island is 'about'. Thus every island is about a topic which is selected, to a degree, by the players. Now, the nature of the conflicts is GM-determined, so its certainly not a case of the islands being blank slates, but the 'proper orientation' of the players to the island, maybe you could call it the 'win conditions' is determined by what the leader declares the signs to mean.
This is really a kind of unique feature of Agon that sets it apart from other Narrativist designs a bit. But in order to understand how this works, you have to be able to accept that it is players who are in charge of this determination, that there are no 'right answers' as to what the signs mean.
I'm not sure who you are saying has failed to communicate. I think the rulebook is clear. I think what you say in your post is also clear, and is - broadly - a summary of and gloss on what is said in the rulebook.
Judging from @Emberashh's posts, it seems that Emberashh's group did not play the game as per the book, but as a GM-driven thing. That would explain why no difference was noticed between Agon 2e and The Green Knight.
It seems to me that both you don't seem to have much appreciation for the creativity I was speaking to in that post, which runs counter to what you both claim to prefer.
And in particular it seems neither of you got that the point of the idea wasn't to stop the mechanic from fulfilling its intentions, but to enhance it and make it more intriguing for everyone. Context is what matters, and arbitrarily receiving them with no connection to the fiction, as we like to say, robs the Signs of the kind of impact they can deliver.
I mean, just answer this: what is more interesting? Being handed a non-diegetic card before you've played, or seeing the Signs of the Gods appear at crucial moments?
And it has to be said, I've read a number of the actual Greek myths as part of coursework, and not just the big name ones. The Gods don't appear to mortals, as signs or otherwise, arbitrarily at non-descript times. They always have context.
Now of course, I'm sure the next argument will be just rolling all of that up into player interpretation, but thats not how the book reads, and you'd have to be coming into the game with the foreknowledge that you'll be making stuff up
And, just for funsies, I will also highlight here that the Book's own play example doesn't do any of that, so neither of you can try and fire back at me acting like the Book actually expects you to add context to the Signs: