So...where did the designation "NPX" come from? I've been asked that question enough times over the years, most recently by a 2012 Polie friend, so I figured it was about time for me to research the definitive answer and put it up on the website...
NPX originated as the U.S. Navy radio call sign, assigned toward the beginning of Operation Deep Freeze...the Navy used/uses 3-letter call signs for shore stations, presumably to make things easier back in the Morse Code days. McMurdo is NGD, Palmer is NHG...Byrd was NBY...oh, and Diego Garcia is NKW...since I spent a bunch of time there I remember that one as well. The old Navy operations orders (OPORDs) for Diego Garcia, Deep Freeze, or wherever, included a communications appendix A in the back that listed all of the codes (I've seen a few of these for Operation Deep Freeze but don't have any copies that include Appendix A).
The designation NPX also appears on some of the old weather forms in the met office. John Gallagher scanned a collection of them during the 2005 winter and shared the files with me as well as the University of Wisconsin.
NPX never is or was an "official" airport baggage code, although in more recent years it has been used as such as well as a tag on APO mail bags (the one at right was sent to me by Scott Smith in 2003), and folks started selling those stickers...
As a more recent bit of official documentation, NSF has still been referencing it, in the official Antarctic Treaty information exchange there has been a communications "Attachment A" which lists the radio call signs (at the top of the pages), equipment used and frequencies monitored by the 3 stations. If you go to the NSF Antarctic Treaty Information Exchange page, the "2007-2008 Plans" page is the most recent one that includes an "Attachment A, Station Communications Forms." Yes, NSF is a bit behind in posting this stuff :) There used to be automated radio beacons at airfields that would continuously transmit the call signs in Morse Code for aircraft to home in on.
Nowadays there are 4-letter airfield codes for the various airfields, kept by the International Civil Aviation Organization (ICAO) (a United Nations organization based in Montreal). Antarctica (or at least the NZ territory) falls under the New Zealand scheme where the first 2 letters are NZ, so McMurdo's airfield codes are NZCM for Williams Field and NZFX for Phoenix Airfield (the now-closed Pegasus Airfield was NZPG). Pole is NZSP. Wilkins Runway, the Australian blue ice runway near Casey, has an ICAO code of YWKS (Australia codes start with the letter Y) and Novo apparently has the code AQ-0001.
The list of 3-letter airport designations used on airline schedules and baggage tags (LAX, CHC etc.) is maintained by the International Air Transport Association (IATA), an industry trade group also based in Montreal. The only Antarctic airfield with one of these codes is TNM at Marsh Base (Chile) on King George Island.
Now, as for that NPX sticker at the top of this page...well, I got mine at Polemart. If you don't happen to be at Pole...I don't know. The Antarctic Connection used to sell them, but they're no longer in business as a store. So download the image at the top of this page and print your own :)