Those are not moons...
...those crescent shapes on the thrones of the King and Queen of Swords, they are sickles. Look at them, they have short handles underneath them. When discussing symbolism so far I've only heard people refer to them as "moons", but they are not!
The sickles are turned away from each other on the Queen's throne but towards each other on the King's throne - where they are framing (trapping?) a butterfly. Why sickles? What's the idea and symbolism behind that? If anybody knows, please tell...
ETA: I'm looking at a standard USGames RWS deck, pocket edition. Don't know how old it is but it's from when they still had the hand-drawn font.