Modern Signs and Symbols
I guess that the main questions are, why are signs and symbols like they are? Who commissioned them? Who decided that yellow was the colour for hazards? Yellow in fact is often used to depict joy, happiness, intellect, energy and riches. Could this symbol of an exclamation mark in fact be trying to get the viewers attention to tell them of riches nearby?
We, of course, know the meanings of these symbols to be common sense, yellow is the colour that is most visible and the colour that is most likely to grab your attention - and an exclamation mark clearly illustrates that there is something to be wary of or that the viewers attention is required. This is the same in every language; however, it is often interesting to question that which we have been bought up to know.