Should a sign be a written message, or should it be something you understand the moment you see it?
I guess it all depends. If you have spent enough money on advertising and if you are the only provider in the country (a government-granted monopoly), you don’t need to explain anything really.
Sometimes a sign is just a sign, and sometimes that’s enough.
But sometimes, a sign needs to be a lot more than just a sign. Sometimes, a sign needs to be a statement.