I was watching an Apple ad, and came across a sentence in which they form the plural of "no" with an apostrophe:
There are a thousand no's for every yes
But shouldn't it be nos? Or is this just for the sake of readability? Like,
We need to dot the i's and cross the t's
Edit: Apparently this has been discussed all over the web.
I would say in this instance it's primarily about avoiding confusion. Use of the apostrophe in general seems to have changed over time. In the past, the use of the apostrophe in abbreviations was commonplace e.g. M.G.B.'s, whereas now, dropping the punctuation points, and discarding the apostrophe, as in MGBs, is perfectly acceptable. The only time the apostrophe is retained is when words or phrases would not make sense without it, such as "mind your ps and qs" rather than "mind your p's and q's" or as here with the use of "no's", since "nos" might be confused with the commonly accepted notion of that as a shorthand for numbers, e.g. "nos 4-9".
The usual plural of no is noes.
Most style guides permit apostrophes for plurals in a few exceptional cases, usually to avoid ambiguity or improve legibility. The only generally-accepted exception is for lowercase letters – mind your p's and q's – and many writers prefer to avoid the apostrophe even there. Some other common (but disputed) exceptions include numbers, abbreviations, and words like do that have an awkward plural form.
The rules for headlines, taglines, and ad copy are a bit looser than for general English, so it's not unusual to see apostrophes for words with uncommon plural forms like if's, and's, but's, no's, and yes's, in addition to the other exceptions listed above. (In the specific case of no's and yes's, they are arguably valid contractions.)
