[Zelandakh]

There is another way of looking at signalling here that is equally as logical and gets all of the messages across. In this the J would show no preference, essentially a denial of anything concrete outside spades. The 10 would be a high card and indicate hearts. The 4 would be a low card and indicate diamonds. The 7 would be a middle card and mean something 'unusual', in this case clearly a club. I understand this is not standard, no need to point it out. However it is logical and this method of thinking (arguably) gives rise to fewer exceptions than standard. Cherdano's method is even more practical with even fewer exceptions!