Check out Bad Apostrophe, Good Apostrophe by rogersgeorge. Here is an excerpt:
I was going to post this Mallard Fillmore comic just because the comic’s funny and about grammar, but it reminded me of a rule: Don’t use apostrophes for plurals.
But English has two exceptions that you might get away with: plurals of numerals and plurals of abbreviations. You don’t need to…
The full article is available here.
