I did some more thinking and ended up with some new ideas:Invert Icon Alternatives
- negative icon, outlined an filled;
- an arrow inverting direction;
- the 'not equal' symbol;
- simply 'Not' words;
- Yin Yang;
I found the thumb-down a potentially universal and simple concept, but I had a hard time trying to make it readable at 16px. That's why I made so many alternatives of it, but don't know which one works best.
So I would like to know what people think fits better as the invert icon, so please share your opinions and arguments.