A little off topic, but the other day I came across a picture of an F6F-5 marked as "NF6F-5" and "V94286":
Attachment:
NF6F-5, V94286.png [ 798.17 KiB | Viewed 1687 times ]
(Source: Francis H. Dean,
America’s Hundred Thousand: U.S. Production Fighters of World War Two (Atglen, Pennsylvania: Schiffer Publishing, 1997), 575.)
This is interesting, because the "N" status prefix for permanently modified test aircraft was a USAF convention that did not appear on Navy aircraft. (In addition, the earliest instance of an "N" prefix I could find after a quick search was an NC-121K so designated in September 1962, so it may have come in with the tri-service sequence introduced that year.
[1] For more on the origins of status prefixes, see a
post in another thread.)
It reminded me of a post on one of Tommy H. Thomason's blogs that shows an F-84 with similar markings:

(Source:
U.S. Navy Aircraft History)
Making the connection even more intriguing is that Mr. Thomason makes the supposition that the F-84s were acquired to replace F6F-5K target drones. So, it's very likely that the same organization that was responsible for the markings on the NF6F-5 also painted the F-84.
So, while they're not technically registrations, they do fall into the category of "multiple instances of odd identification markings on American-built military aircraft".
EDIT (24-12-03): Another couple aircraft with the "N" prefix, in this case NFG-1Ds, show up in a
post about US Naval Air Reserve markings by Dana Bell.
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