It’s the question on everyone’s mind. (Alright, maybe not everyone, but people have certainly noticed and brought it up.) This is, of course, assuming that it’s a ship. Still, let’s go ahead and make that assumption.
Certainly it is made to look like a pair of legs. That would be a very new kind of Gem ship though. We’ve seen two Red Eyes and several Roaming Eyes, but the only other anatomy-based ships we’ve seen have been from the upper-body: the hand ship Peridot and Jasper arrived on Earth in, and the Diamonds’ own arm ships.
Based on that alone we’d expect the pink ship to likewise be an arm ship (or at least a hand). Still, it’s interesting to note Blue and Yellow’s position on the Diamond Authority symbol: they occupy the middle, while White occupies the top and Pink occupies the bottom; Blue and Yellow even have their gems at arm level.
Perhaps, then, White Diamond’s ship (she may not have one, but the Gems could have established a pattern as though she does) would be a head and the eye-based ships we’ve seen are to it as the hand ship is to the arm ships: lesser designs that pay homage to a Diamond’s (real or hypothetical) vessel.
Besides, who remembers Arcade Mania and the giant foot? If Pink Diamond has a leg ship, then surely there must have been foot ships as well.
That said, there are still good arguments for it being an arm ship as well, if we were to leap to the conclusion that this must be Pink Diamond’s own ship. Just to get one out of the way: wouldn’t a pair of legs flying through space just be silly? Yes, arms are strange too, but the show has already successfully made those normal.
The more serious reason though: scale. Again, if this is actually Pink Diamond’s ship (which, we must admit, we can’t be sure of), it would have been enormous. Look at Blue Diamond’s ship: that mark in the center of the hand is large enough for her palanquin to enter through, and each finger is much wider than that mark.
Using Steven and Lion for scale on the pink ship, and the palanquin for scale on Blue’s ship, those two appendages we can see would be about right for fingers on Blue’s ship.
Those appendages are also far larger than those on the hand ship from The Return. They’re obviously too long to be toes. The way we see it, based on ship shapes we’ve seen so far, it can only be either a small leg ship or a large arm ship.
Until that ship comes out of the sand, however, we won’t know for sure. We only have our guesses, things we can work out based on what we’ve already seen. That’s why, for now, it’s a mystery.