The proper use of apostrophes when denoting plural or possessive nouns is the subject of many tutorials, especially the rule-breaker “its/it’s.”
But there should be no debate about whether acronyms or other all-capitalised or numeric constructions should include an apostrophe when made plural: they shouldn’t!
Public Enemy #1 – “FAQ’s”
The acronym “FAQ” stands for “frequently-asked questions,” and you’ll find it everywhere on the web. Though it’s often correctly written as “FAQ” (or used in constructions like “Read our FAQ,” etc.), you’re just as likely to see the incorrect “FAQ’s” (or “FAQ’S,” which is both incorrect and weird). You’ll even see it on U.S. government pages. UK gov has it right everywhere.
“FAQ’s” is wrong because the author intended to describe a list of many questions and their answers. That would be: FAQs, where the absence of an apostrophe makes the s in FAQs plural. (The question of whether an s is necessary at all is a different issue; personally I have no problem with it.) When written with the apostrophe, it becomes possessive. Creating a plural or possessive form of an acronym is done just like any other noun. Yet writers who would never slip up and write “Click here to read about our car’s!” often do write “Click here to read our FAQ’s!”
Public Enemy #2 – “The 80’s”
No, not specifically the 80s (which were awesome), but the plural form of any decade, such as “in the 1960s” or “the roaring ’20s.” When used in this form, the decade becomes a plural noun and should be treated as such.
Some examples (including a singular year for comparison): “New wave was the second-best thing about the ’80s; the first was the Smurfs!” “I’m wearing this stone-washed denim jacket and these parachute pants to the ’80s party tonight.” “Ronald Reagan was nominated for president in 1980.”
If there were a case of a possessive decade—which is certainly more rare—it would be written as: “Those are the ’80′s Pop-Rocks!” (Meaning, the Pop-Rocks belong to the entity 80s.) Luckily, there’s not much call for this construction, which makes it much easier to spot the incorrect plurals containing an apostrophe before the s.
Public Enemy #3 – “From the low $300’s”
Homes’ starting prices should not include apostrophes. You’ve probably examples of this mistakenly-placed apostrophe yourself on many of the real-estate development signs clustered around busy intersections like a patch of over-zealous mushrooms. “Prices from the low $300′s” or “Homes starting in the high $200′s” these signs exclaim. Wrong. Not the prices themselves (though they sure seems that way sometimes), but the apostrophe.
Style, Value, Location and Improper Apostrophes. Generalised price points like these should not include an apostrophe. As with decades, including one turns the number from the writer’s intended plural meaning into an incorrect possessive meaning.
The correct plural-vs.-possessive use of apostrophes can be tricky for some, a fact I blame largely on its-vs.-it’s, whose proper usage seems backwards to the rule for most other words. (“it’s” is a contraction of “it is” or “it has” instead of the possessive form if “it.”) But when it comes to plural acronyms and numeric constructions like “the ’60s” or “starting in the high $100s,” I think the cause of the incorrect apostrophe use is simple: people just don’t like seeing an s following a capital letter or number.
To them, it just “looks wrong” so they drop an apostrophe in to separate them. (It’s for the same reason some people write “Monday’s” or “Saturday’s”: they don’t like the look of the plural-creating s right after a capitalised word. Of course, this is wrong—unless they’re talking about the restaurant TGI Friday’s.)