It's not quite the same as national insignia, but I found it curious that someone applied the registration to this Boeing 707 with a dash in it. It might be explained by the fact that it later went to Australia, who use the dash in their registrations:

(Source:
Aussie Airliners)
It's actually interesting when you realize that
more countries in the world use letters instead of numbers in aircraft registrations and the United States is kind of the odd one out. I think a dash makes more sense when there's only letters.
Also, I recently came across this apparent mistake in designation on a C-46R, or should I say "C46-R":

(Source:
Airliners.net)
Although, I guess since it is technically a new variant built by Riddle, they could call it whatever they want.
EDIT: Also, for some reason it was a common thing to try to squeeze the entire serial number on the vertical stabilizer of the BT-13 and not let it run over onto the rudder. I'm not sure why this was a thing, but if I had to guess it was some combination of the fact that swapping out a damaged rudder would have caused confusion by losing the last few digits or a leftover of the early paint scheme that had the red, while and blue rudders that would have made a number hard to read:

(Source:
Wikimedia Commons)
You even get these weird diagonal serial numbers where they try to force them to fit:

(Source:
Aircraft Wrecks in Arizona and the Southwest)
Here's one where you can still see the ghosting of the number on the rudder:

(Source:
Age Photostock)
What makes it so strange to me is that no one else seemed to ever have those concerns. I mean just about every other American warplane was fine with dividing the serial number between the stab and rudder.
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