Dear Mister Language Person: What is the purpose of the apostrophe?

Answer: The apostrophe is used mainly in hand-lettered small business signs to alert the reader that an "S" is coming up at the end of a word, as in: WE DO NOT EXCEPT PERSONAL CHECK'S, or: NOT RESPONSIBLE FOR ANY ITEM'S.

Another important grammar concept to bear in mind when creating hand-lettered small-business signs is that you should put quotation marks around random words for decoration, as in "TRY" OUR HOT DOG'S, or even TRY "OUR" HOT DOG'S.
—Dave Barry, American humorist, Tips for Writer's