Yellow Diamond would have a longsword.

In sworn to the sword, we see statues and symboles that may represend the diamond leaders

The pink one is smashed and so is her statue but we’re just using that to get our barrings. if they are in the same position ass the floating diamonds, the left one would be yellow. 

Notice the shape of the head. now look at the extended intro that showed a teaser for who may very well be yellow diamond.

Originally posted by mayeverbee

It has the side locks that wrap around her cheeks before coming out into a point. So my theory is that Yellow Diamond would have a sword weapon to contrast Roses shield.