You could have made your second post in this thread.

http://www.geting.se/image.php/203621-2 ... 02_400.jpg


I thought it was some kind of "temporary/in transit" plate?

My understanding is that they are temporary plates used by car manufacturers to drive non-production cars on streets. Great deal of paperwork required to request such to city/government. In Japan test vehicles are not allowed on streets vs. USA where they are allowed with special MFG plates owned by each company.

There is an explanation at:
http://www.tigerdude.com/japan/license/temp.html

That may be theory, in practice they are most often seen on cars being offered for sale or at car shows and racing events. Could be people with dealer licenses throwing a temporary plate on their unregistered antique car or race vehicle in order to drive it to and from the show or track, or dealers to take the cars they are offering for sale to a car show where they might find interested buyers.