Error page illustrations
Illustrations of errors with different shades of "wrongness". Again, metaphors from the real world come to the rescue, such as signs or a siren. And if something is broken, it looks really sad=)
Still I think that icons alone will not be a universal language. Only in combination with short explanations in the form of words. Or is it possible to have a universal understanding only in the language of icons?
This set you can buy here: