Abbreviation of “number”

You should just keep the abbreviation No. for both singular and plural.

We often just use the number sign # in North America. Why not?

I would say this one is more a matter of personal or house style, like whether to add commas to addresses etc in business letters. Personally I would capitalise and probably not use a full stop (period) - No 1. And I would use Nos 1-3 for plurals. But I don't think there's necessarily a right or wrong way. Although not North American I also use the hash sign in informal notes, but I wouldn't use it in more formal work.

I write a language blog for learners, with exercises which obviously have numbers, and with questions that also have numbers, but I hardly ever have to use the abbreviation No - for the questions I just use 1,2,3 etc and if I need to refer back to them, I refer to them as Question 1, or Questions 1-3 etc. But I suppose you still have the same style decision to make there, too.

The abbreviation is just about what your sort of personal style is. If you try to make the sentence sound as short and to the point use he # sign. If you want to make your sentence legnthy, then use the whole word. For the abbreviations, North America usually uses the No. for both singular and plural, but really it soesn't matter.

What a mess abbreviations have become. This may be my practical side but I personally do believe the "No" is extensively overused, I believe this because it is a very general abbreviation which usually refers to something more specific. Usually a number should represent something like an index, line, position, etc. and in most situations it should be appropriate to use a more descriptive title. In technical applications like Databases titles, Spreadsheet or Table headings, etc. I would urge against this temptation. I'm guessing it became popular back in the 60s and 70s every big name ended in Co.

I would only use the No abbreviation as part of a name or quote where the context is clearly stated, as in "Bus Stop No 3".

For those of my generation (ahem) the plural is nos. either with a capital or without. It's a usage I haven't seen in quite a while.

Often times when I see the abbreviation for number, it has a period after it with a capital n so you can identify it from the word no.
Example: No. 15

Just my personal opinion, but I say that abbreviating makes things more confusing, and you might as well just say or write the whole word.

Just for a change, any comments on N° for this abbreviation.

Awe.....Hell NO........

LOL

Thank you for existing.

For all my trivial existence, the wrong, yet pervasive mispronunciation of the Prepositional Function word "for", never fails but to poke me in the eye.

If every man, woman, and child insists on mispronouncing this critical, extensively used Function word "for" as "fur", then why not change its spelling to accommodate their otherwise misuse?

Disgruntled, yet pleasant,
BillyBob

For a set of engineering/design plans and documents, the correct denotation would be "no.s"