But I think that at first this might create even more confusion, since people won't be able to read it "at a glance" when they meet it first time, they would need to understand "what that even is", and that creates friction and stops adoption.
So I think for such an idea to take off, it must be as immediately obvious as possible. "A2b" is not immediately obvious. Maybe the answer is something like "use only text descriptions that are easily understandable, but also code their values with font colors, so when a person familiar with the rating system opens yet another repository, they can quickly understand the content without reading, just by seeing three font colors".
The ACR.md file itself has the rating and a quick writeup on how AI was used, but now I'm wondering if setting up something like aicoderating.com/A2b to see that specific rating explained would be helpful.
I actually thought about other ways to differentiate this (eg. colour), but if it's not plain text it will make it hard to use in certain places, and it could also cause accessibility issues.
Either graded from A-E (A being excellent, E being poor) and you can break down that score from your three character disclosure.
I actually started toying with single letter ratings to start with, but there are some issues with it. Giving something like a single letter grade to a repo has to make judgement calls about AI, which is something I'm trying to avoid with ACR. Some people won't touch any AI code, and others are ok with it as long as someone knowledgeable reviews it, and a single score would have to pick one of those views for everyone. The idea is to give a few key points and let the reader decide what that means to them.
A single score also kind of hides what people may be looking for. For example, an A3a (an expert wrote most of the code with AI and checked every change) and C1e (very little AI code but nobody checked it) could end up with the same grade. A multi-character rating seemed to offer up more information at a glance.
If you want a single pass/fail, you can still get one by setting your own minimum for each part, like "Oversight b or better", and any rating either meets it or doesn't.