Punctuation in Abbreviations

Bill asks:
When abbreviating something, such as the United States, when did it become acceptable to abbreviate it to US instead of U.S.?

Abbreviations can be shortened versions of words (etc.) which we pronounce in full (et cetera); they can be acronyms, which are pronounceable (UNESCO, AIDS); or they can be initialisms, which require us to pronounce every letter. In common acronyms and initialisms, the periods tend to drop out: F.B.I. becomes FBI, R.C.M.P. becomes RCMP, and so on.

This is a matter of changing usage, and it's still perfectly OK (or O.K.) to keep the periods in. But in our impatient age, when every keystroke counts, many people prefer to drop the periods.

This is not universal, however. The Canadian Press Stylebook, used by many journalists here, recommends keeping periods in geographical abbreviations and initials of persons:
B.C., U.S., L.A.; J.R. Ewing, E.T.

But it also acknowledges that well-known public figures may become known by initials without periods: JFK, FDR, W.

The Stylebook also offers the following advice on punctuating abbreviations:

Write compound abbreviations without spaces:
M.Sc., P.Eng.

Omit periods from currency abbreviations:
$500 US, $800 Cdn

Put periods in most lower and mixed abbreviations:
f.o.b., Jr., lb., Mrs., m.p.h., B.Comm.

But metric symbols are technically not abbreviations and they don't take periods except at the end of a sentence:

m, km/h
His weight is 80 kg.

Mixed abbreviations that begin and end with a capital letter do not take periods:
PhD, PoW, MiG, U of T

Single-letter abbreviations take a period:
127 E.(for East) Fifth Street

Letters themselves, however, don't take a period:
Brand X, the letter J

Comments

[Csilla]

I'm a Hungarian girl and I'd just like to know the meaning of the following abbreviations:
O Level / GCSE
A/AS Level
HNC
HND/BTEC

thanks

[Crawford Kilian]

Thanks for your question, Csilla—I've often read these abbreviations in British periodicals without really understanding them. In finding the answers, I also found Answers.com, which is now at the top of my "Useful Links" in the left-hand column.

O levels are the basic level of a school subject.

GCSE stands for General Certificate of Secondary Education.

A/AS level appears to stand for Advanced/Advanced Supplementary, recognizing a fairly wide mix of subjects that have not been taken in great depth.

HNC is the Higher National Certificate, awarded after reaching some level of post-secondary. One level higher is the HND, Higher National Diploma, which is one step below a bachelor's degree.

BTEC stands for Business & Technology Education Council, a subdegree evidently awarded for students who concentrate on subjects outside the usual academic programs.

Thanks for advancing my own education!

[Val]

What does the Canadian stylebook say about the punctuation of Ms Jones--is it incorrect to put a period after Ms?

Thanks

[anne]

What is the preferred plural form of the abbreviation for "cash on delivery" (c.o.d.'s, CODs)?

[Janice Doyle]

Has abbreviating A.D. and B.C. changed with usage as other abbreviations have?

[Sandra]

When the last word in a sentence is an abbreviation such as P.C., does one use only one period or two?

Example:
We thank the law firm of Johnson and Johnson, P.C..
or We thank the law firm of Johnson and Johnson, P.C..

[Crawford Kilian]

One period at the end is all you need:
We thank the law firm of Johnson and Johnson, P.C.

[Susan]

Is it A.M. or AM or a.m.?

I have seen it so many ways.

[Barbara Kevorkian]

In a sentence that has a clarifying phrase in parentheses that ends with the abbreviation, etc., do you put the period for the sentence outside of the parentheses, so it looks like this: (...etc.). or would you drop the period on the etc). or do you leave the period off?

[Crawford Kilian]

First, consider whether you really need to end a sentence that way!

But if you must, then (...etc.). is the correct punctuation.

[umaira]

is there any abbrevation for the word TEACHER?

[Crof]

What a good question! We do have Prof. for Professor, Instr. for Instructor, and so on. But I can't recall an abbreviation for teacher.

[KristinaC]

What about when there is a comma next to the abbreviation? For example: "The countries competing include the U.S., the U.K., and China."

Is that correct? Or is the second period omitted?