...if taken seriously, have usually been considered signs of immaturity or lack of common sense. (Para. 2)
a sign of/signs of: something that shows the evidence of sth.
another sign of a person's nature (Para. 9)
A nod is a sign of agreement. 點頭就是表示同意。
Words are the signs of ideas. 詞語是思想的符號。
common sense: the ability to behave in a mature way and make practical decisions
Sometimes we guess the meanings of unknown words or expressions in a reading passage through common sense. 有時我們通過常識來猜閱讀文章中的生詞或詞組的意義。