To Apostrophe or Not To Apostrophe

TOSC reader David H. from Virginia Beach, Virginia, asks:

If I were to write about buying more than one compact disc I would write "I bought 17 new CDs." Is this correct? What makes me ask is that we were on I-95 today and I saw a sign that read "RV's and Trucks Welcome." The apostrophe s marks possessive, right?

The apostrophe-s does indeed denote possession. It's a rare case that an apostrophe is used for a plural, but it happens. "I got two A's and three B's on my report card" is an example of how apostrophes help to clarify the plurals of single letters. But this is an exception to the rule.

For acronyms, the standard is to pluralize them with a single s, although this standard is not particularly standard, especially among highway sign workers.