I agree that drivers should know not to reverse on a highway regardless of local signage.

But in situations that could be ambiguous, I think this is a regional difference - the US, Australia, part of the rest of the Americas use lots of text on road signs (including literal "wrong way" signs); Europe and much of the rest of the world use far less text (including purely pictographic "wrong way" signs). Especially important in Europe where drivers just can't learn 20+ languages.