Does this question Basic algebra of $\mathcal{O}_0(\mathfrak{sl}_n(\mathbb{C}))$ — Reference request look like this for anyone else?:

Those squares are supposed to be \mathcal{O}'s. As far as I can tell the LaTeX code is fine but it is rendering wrong for some reason. I remember looking at this question a couple days ago and it looked fine.

EDIT: Maybe I should say I'm on Chrome on a Mac.

EDIT 2: Changing the math renderer (as mentioned in the comments) fixed this for me; thanks!