The questions says it all.
Genaro
Well, people should really say “PIN” instead of “PIN number”. It drives me almost as insane as “NIC card”.
The term was invented by the Department of Redundancy Department.
Right, and it is called an “ATM” not, an “ATM Machine”.
Both are quite common it seems.
No, one should only use a PIN number on an ATM machine … unless, of course, one does one’s banking online on a PC computer.
The PI Number is 3.1415926535 8979323846 2643383279 5028841971 6939937510 5820974944 5923078164 0628620899 8628034825 3421170679 8214808651 3282306647 0938446095 5058223172 5359408128 4811174502 8410270193 8521105559 6446229489 5493038196 4428810975 6659334461 2847564823 3786783165 2712019091 4564856692 3460348610 4543266482 1339360726 0249141273 7245870066 0631558817 4881520920 9628292540 9171536436 7892590360 0113305305 4882046652 1384146951 9415116094 3305727036 5759591953 0921861173 8193261179 3105118548 0744623799 6274956735 1885752724 8912279381 8301194912 9833673362 4406566430 8602139494 6395224737 1907021798 6094370277 0539217176 2931767523 8467481846 7669405132 0005681271 4526356082 7785771342 7577896091 7363717872 1468440901 2249534301 4654958537 1050792279 6892589235 4201995611 2129021960 8640344181 5981362977 4771309960 5187072113 4999999837 2978049951 0597317328 1609631859 5024459455 3469083026 4252230825 3344685035 2619311881 7101000313 7838752886 5875332083 8142061717 7669147303…
This topic comes up all the time and peoples’ answers are always what they have already been in this thread.
All wrong.
The normal progression of English is to use the acronym as an adjective describing the noun that is the last word in the acronym.
PIN Number. ATM Machine. (Please don’t bother to nitpick that PIN is an acronym but ATM is an initialism. That’s exactly as pedantically incorrect as objecting to PIN number in the first place. The word acronym in both senses in completely correct in all types of writing, from casual internet speech to formal works.)
OPEC Country. Note that this means that OPEC Nation is incorrect.
There is nothing inherently wrong with redundancy. It’s as much a part of the normal speaking language as eliding sounds to make words shorter. Many of the words and word combinations we consider entirely unexceptional today were originally introduced into the language as redundancies and intensifiers to make the language stronger or more understandable.
A great book on the subject is The Unfolding of Language (An evolutionary tour of mankind’s greatest invention), by Guy Deutscher. He uses numerous examples of how these processes have shaped English - and all other languages - over the entire course of their existence. This is the way language works. This is the way normal users use language. The illiterate pedants, as I call them, know everything about English except for the way it actually works. Ignore them and you can learn an amazing amount.
That was a very interesting post. If I may be permitted a slight hijack, would you consider something like MLB Baseball fitting this as well? To me, it, ah, “seems” like it is slightly different, but I can’t really put my finger on why.
They’re all examples of Redundant Acronym Syndrome - RAS Syndrome for short.
People don’t tend to actually say MLB, though. It’s abbreviated in print, but spoken as “Major League Baseball.” Unlike the NFL and NBA, which are often called “NFL Football” and “NBA Basketball.”
NFL football is distinct from NCAA football, or flag football, or football/soccer.
A good portion of the people I know say PIN and ATM.
Examples:
“Oh my god I’ve forgotten my PIN!”
“Honey, stop by at the ATM and get us some cash please.”
A strawman, mostly.
Your post accurately describes the way language is often used, but is anyone disputing what you say? Is anyone here saying: “No, people do not use redundancy in speech?”
Clearly they do.
The question is whether it would be better if they didn’t. This is of course a value judgement, so there is no right answer. But if you can come up with a coherent argument as to why it is in any way useful to say “PIN Number” when “PIN” will do, or why it is not marginally more efficient to say “PIN” rather than “PIN number”, let’s hear it.
If it was a PI number, it would be too easy to guess, but it would take a long time to type in.
I rarely say “PIN number”, and most ATMs just say “Enter your PIN.”
(Though I prefer the ones in France that instruct you to “Composez votre code secret” - it adds a bit of mystery to the proceedings 
)
Especially if one banks at UMB* Bank.
*United Missouri Bank.
The answer to this question, along with many others, is short and simple: People are stupid, that’s why.
Compared to what?
You’re saying that ATM is an acronym? Unless people are pronouncing it as at-uhm or something similar- it’s not.
How should I know? I’m just a stupid person… 
I would venture that people are stupid compared to their own intellectual potential, usually on purpose.