Words are symbols. The word 'dog,' for example, stands for an animal with given characteristics. It can be used metaphorically with a derogatory intention. Instead of the word, a drawing of any variety of dogs may be employed as their symbol. Thus, the signification of a picture is analogous to the denotation of a word.
Signs are indications.
They may be artificial or natural . Symbols of a man or a woman are common as signs in lavatories. On the other hand, fever is a natural sign of disease. The changing pitch of a whistle is a natural sign of a fast traveling locomotive. A sign has to be interpreted, while a symbol has a meaning by itself.