Tests
Nero did not know if his friends could understand his vague code, but it shouldn't have been hard. Aether was pretty common, and would usually be the first thing people think of when they see an A.
But that is not what he was focusing on. Instead, he focused on determining if his aether was being consumed. Even though he suspected that not many would be able to last the full hour, Nero intended to last the full hour and have energy remaining to do whatever came next.
There were many things he couldn't guess about their situation, but there was at least one thing he was absolutely certain about, and that was that they were being observed. When he and the rest stood in line with discipline, they were being observed. When they accepted the punishment without protest, they were being observed. When he flashed the symbol with his hands, he was being observed.