From what I understand, it is common to use a line above the symbolic expression denote the closure of an mathematical object, e.g. if $K$ is a field, then usually its algebraic closure is denoted by $\overline{K}$ (or $\bar{K}$).
For a symbolic expression that contains a sub- or superscript, do you include the sub- or superscript or not? As an example, if $\mathbb{F}_q$ denotes a finite field, do you indicate its algebraic closure by $\overline{\mathbb{F}_q}$ or $\overline{\mathbb{F}}_q$?
I have always written $\overline{\mathbb{F}_q}$, but I recently received some feedback stating that it should be $\overline{\mathbb{F}}_q$.
Logically the first should be the "rightful one" in the sense that $K = \mathbb{F}_q$ so $$closure(K) = \overline{K} = closure (\mathbb{F}_q) = \overline{\mathbb{F}_q}$$.
However the second is more accurate in a typographical sense, so I would use the second. Since you can't make misunderstandings, you should (I think) use the second one.
All I have for reference that is "agreeing" with me is a very long pdf about french typography...
In the end it is not very important, but you should choose one and stick to it, and each time you introduce $\bar{F}_q$ in your document (for the first time) say that it is the algebraic closure.