While in Marks & Spencer's over the weekend, I saw a sign saying
"Women's mac's half price".
My wife thought that there should be an apostrophe in "mac's" as it was plural rather than possessive. I said there should be, as it was an abbreviation of "mackintoshes".
I'd say that you are correct in saying an apostrophe is appropriate due to it being an abbreviation.
I'd also be willing to bet that the person who wrote the sign got it correct more through luck than judgement and they were probably misusing the apostrophe for a plural
I'd not have put one in because I'd consider mac to now be the word used, whether it used to be an abbreviation or not. But I can see the argument the other way.
There should be NO apostrophe in macs here; it is a simple plural, despite the fact that mac is an abbreviation. In the 'mac' form, it is an independent word in Chambers Dictionary and in the 'mack' form, it is an independent word in The Oxford English Dictionary.
I don't because I believe it is neither logical nor consistent. But I believe I read somewhere that the power that be (whoever they are) decree you should.
CDs should be exactly as you wrote it, Helly...ie with no apostrophe. It used to be 40/50 years ago, that such pluralised acronyms would be written WITH apostrophes. For example, "Three QC's represented him at trial" or "There are five MA's on the school staff." Nowadays, however, they are generally omitted, except where their absence might cause confusion. For example, "There are four i's in Mississippi." If that had no apostrophe, it might be read as four is.
The abbreviation argument is nonsensical. You don't put an apostrophe in the plural of mac just because it is an abbreviation of the plural of macintosh - by that argument, you would have to put an apostrophe at the end of the singular noun too.
E.g. "The woman was wearing her mac' because it was raining" is incorrect.
Therefore, by extension, "Women's mac's half price" is incorrect for exactly the same reason.