@pastanaga - I don't know, I think that people assume too much sometimes when they think that visual metaphors are universal. Traffic signs are a good example. There are plenty of them that confuse foreigners because they don't seem to make sense, while the people who are used to them think of them as perfectly obvious.
Color is another really good example. A lot of people think black is a universal metaphor for death, but in a lot of cultures it's another color, like white for example, that is considered the right one for funeral garb and so forth. Visual metaphors are not something to be taken for granted as obvious.