In response to a recent comment from Linda on an earlier post, I have gathered here my previous apostrophe posts and will attempt to cover any ground I've missed among them. I had intended this post to rely heavily on these earlier examples, but I discovered, to my chagrin, that I hadn't ever written a really basic piece about apostrophes. I intend to correct that oversight here.
If you are anything like me, you'll find one use of the apostrophe confusing. Sources consider it appropriate to use the apostrophe when indicating more than one lower case letter, as in “mind your p's and q's”. You need not include the punctuation when talking about more than one capital letter (Ls), number (7s), or symbol (?s). I don't understand that rule, but I include it here for completeness.
I hope that answers your questions, Linda, and gives you an idea of what you can and should not do with apostrophes. If anyone needs more clarification, please drop me a note below and I'll answer them in the near future.