Initially I was going to argue the bolded as my reason, but your edit assumes the point of icons is to 'convey information' which isn't necessarily true for what AA signs need to be.
Hands down, Reach's AA icons do a fantastic job at showing you what the AA does. No arguments there. There never was.
There does not need to be any information conveyed as to how it works though. Like I said, the icons for every single weapon does not tell you how it works.
Bungie took a literal representation to AAs so as to show users how they work at a glance.
343 has taken a more symbolic approach to representin AAs. Now, if the purpose of these icons is to convey how the AA works, then of course, failure (to some extent). My whole point is that we don't need to be spoonfed what AAs do. They are indexes really. If the indexes are too similar, then, as I have already said, they will not work.
The long and the short of it; I don't believe signs need to tell you how the things work. As long as they are clearly identifiable as whatever they are, that's all that matters to me.