The Oxford Companion to the English Language cautions strongly against the use of what it calls the illiterate “Greengrocer’s Apostrophe.” What that means is an apostrophe needlessly inserted to make the plural of a word—a practice for which British greengrocers (and maybe a few elsewhere) seem to have a penchant, as in:
FRESH PEA’S AND BEAN’S
Lynne Truss in her inexplicably best-selling Eats, Shoots & Leaves, has made a virtual career of ferreting out needless apostrophes, citing such horrific instances as:
CD’S, DVD’S, VIDEO’S, BOOK’S
The most egregious example surely must be the BBC web page announcement of a program about grammar for children, which read:
NEXT WEEK: NOUNS AND APOSTROPHE’S!
To be perfectly fair to those beleaguered greengrocers, I must point out that in the sixteenth and seventeenth centuries, before the Mrs. Grundys of grammar started making hard-and-fast rules, there was a perfectly respectable tradition of using apostrophes for plurals, especially for words ending in vowels--“We doe confess Errata’s” (Leonard Lichfield, 1641), “Comma’s are used” (Philip Luckcombe, 1771)--and for words ending s, z, ch, sh, tz (“waltz’s and cotillions”). In these rule-ridden days, however, using an apostrophe for plurals other than numbers (7's), letters (W's), initials (B.L.T.'s) and a few oddities like “do’s and don’ts,” is definitely among the don’ts.
The Bard of Buffalo Bayou, who has apostrophized quite a bit in his time, is indebted to the rhythmic genius of the immortal Joyce Kilmer for the following:
I think that I would rather be
A dash than an apostrophe.
A dash is simple, strong, and firm,
Apostrophes just make you squirm.
But if somehow I had to be
A stupid old apostrophe,
I’d keep things strictly intramural
And never show up in a plural.