We have learned through experience that dark clouds may signify rain or that a loud voice may indicate anger.
As a child I thought that clergy were always angry because they preached in loud voices. Sometimes signs are learned by simple conditioning principles, as in the case of Pavlov's dog who learned that a bell signified food.
Below, in the notes, are some examples of street signs that posses many of these qualities we have been discussing. How many of them can you read ?
So, if all these modes of communication which are based on signs, as important as they may be, are NOT language, then what is language?