What icons would be better to distinguish between knowing an answer or not?

I know the headline might not be that explanatory, so let me elaborate. I have a website with some different questions, for which you can get the answer revealed if you click on a button.

So that looks something like this:

Now, for each question I have I would like to know if the person reading it knows the answer to this question or not, by placing two icon above or below the box (have no decided yet). However, I am having a hard time to decide what icons are actually the best way of "asking" this. I've tried with thumbs up and down, but in some way, that seems more like a question about whether I like this question or not - not if I know the answer. The same goes for a checkmark and a cross. So which to icons would you recommend in a situation like this?