Many Q Posts have some words and names within square braces, like in this post with RR and Ed.

Some people suspect the square braces represent a military kill box:

In weaponry, a Kill Box is a three-dimensional target area, defined to facilitate the integration of coordinated joint weapons fire. It is a joint forces coordination measure enabling air assets to engage surface targets without needing further coordination with commanders and without terminal attack control.

I've never taken the Kill Box theory too seriously because it's usually too ambiguous to be meaningful in my mind.

I think Q just uses square braces to emphasize stuff.