Readers of the math magazine Chalkdust voted on their top 10 mathematical symbols. See the list here: http://chalkdustmagazine.com/regulars/top-ten-issue-02/
BADGING: Read the entire list. Pick out two symbols that you hadn’t seen before reading the article. Research the symbols using Wikipedia or Wolfram Alpha and write a couple sentences for each symbol explaining what it is used for in mathematics. Then, pick out one of your favorite mathematical symbols that doesn’t appear on the list. Explain in a couple of sentences why you would choose it and where you put it on the list.