Q. When using the plural of “ad,” i.e., “ad’s,” is it incorrect to use the apostrophe? The three-letter string “ads” just looks so wrong when typesetting it. Would appreciate your guidance.
A. “Ad” is just a regular word, and the plural “ads” is also regular, so there’s no need to mess with it. Plurals almost never take an apostrophe. Chicago style uses an apostrophe for the plural of upper- and lowercase single letters (the three R’s, x’s and o’s), but for little else (for instance, we write “dos and don’ts”). Please see CMOS 7.15 and 7.66–74 for more examples and exceptions.