I've spent some time searching here and also remember from the past that the registration/serial numbers we're supposed to input here are the ones actually displayed on the aircraft, even if it's a fake registration applied as in the case of certain display aircraft.
I happened upon a rare opportunity recently, a cache of museum planes that somehow haven't yet made their way onto Airliners.net. Some of these aircraft have fake serials. An example: I have an Air Force F-102 that I know from research is 53-1787. However, painted on the tail is 62334.
If I input this into the database using the rule as I understand it, the 62334 should be used as the serial and I should reference 53-1787 in the remarks. The question is, should I use 62334 as-is, or translate it to the format of a real Air Force serial, which in this case would be 56-2334?
FYI, the real 56-2334 is listed on Scramble and on Joe Baugher's site as having gone to the Turkish Air Force, while 53-1787 is listed on both sites as being in the place where I found her.
[Edited 2012-10-09 09:48:41]