Take another look at the store signs mentioned at the beginning of this section that incorrectly used an apostrophe:

The words that have apostrophes are just plain ol' plurals; they don't show ownership in any way and so don't need apostrophes. (If you're unsure about whether you should use an apostrophe, ask yourself if the word in question owns or possesses anything.)

Also, if you have proverbial expressions that involve individual letters or combinations of letters, use apostrophes to show their plurals.

In these examples, some style academic or company guides dictate that you shouldn't italicize the letter you're making plural; other guides take the opposite view. Be sure to consult the guide suggested by your instructor or company.

Another time that you should use an apostrophe to form a plural is if your reader would be confused by reading an –s alone (for instance, when an –s is added to an individual letter or letter combination or to numbers used as nouns).