The answer to the blank space is signs and symbols.
Sign and symbols here refer to distinct sociological concepts. Sign is defined as a form of language used by group of people. Signs are usually universally understood by most people, which in this example might come in the form of telephone sign, which both the grandparents and the young grandchildren perceive the same way – as something related to the telephone. While symbols are perceived differently be people from different cultures, or even generations – such as the emoticons used by the grandchildren, which the grandparents do not perceive the same way.