I’m gonna add something to this that I haven’t seen anyone talk about: The circles around the Diamonds are all the planets and moons they’ve colonized under their name. The score at the time the Moon Base was created seems to be: Yellow Diamond: 8 planets (2 in her hands) and 15 moons. White Diamond: 10 planets (11 assuming the one in her hands is a planet) and 4 moons. Blue Diamond: 4 planets and 3 moons. Pink Diamond: 1 planet and 1 moon, almost definitely Earth and Earth’s moon. So assuming the amount of planets one Diamond commands is indicative of her power/authority, White Diamond is at the top of the pecking order, followed by Yellow Diamond, then Blue Diamond, and lastly Pink Diamond.
That makes sense given the symbol:
My guess is, because of the emphasis on it, the planet in White Diamond’s hands is Homeworld itself. While all the diamonds rule it, it wouldn’t surprise me if White Diamond wanted a reminder that she was the one truly at the top.