A math symbol in quotation marks

Question

As to quoting math symbols, we already find nice answers in How to write quotation marks in math environment?

But I have a question to a problem that doesn't show up in the examples in the above article: What's the best way to enclose a single math symbol in double or single quotation marks with proper spacing?

\documentclass{article}
\begin{document}
``$R$'' or $``R"$ or \textit{``$R$''} or \textit{``R''} \dots
\end{document}

In the first two, the opening double quote is a bit too far from "R" and the closing one is a bit too close. The third and fourth ones are better but you still see asymmetry (the closing quote is a bit too far). Is there a standard solution? What do people do in this situation?

Edit: I ask this question because I very often write things like

In the above equation, ``$R$'' stands for the ratio of . . . 

You could argue that a simple $R$ without double quotes is good enough in this example because "R" is italicized, but I often feel the emphasis isn't conspicuous enough.

Edit 2: I corrected my description of the third and fourth examples. At first I thought they look different, but LaRiFaRi has made me realize that they are identical! Sorry for the confusion.

Answer 1

The first two are the same. And so are the last two (both times possibly taking different fonts. But math and text font do not differ here as far as I see). But the last two are having slanted quotation marks. Do you want that? If yes, try italic correction such as \textit{``\/$R$''}.

Personally, I would go for the very first one. It has the best syntax and does not look too bad. If you use it in just a few cases and you dislike it, you may type ``$R$\kern.3ex'' or alike.

In every case, I would recommend a custom command for such things. Like this, you stay absolutely flexible for later changes.

% arara: pdflatex

\documentclass{article}
% this package enables you to change your quotation style afterwards. 
\usepackage{csquotes}
% with this command, you can add a kerning to all possible math quotations and of course change or delete them later, if you change the font or dislike your first chose.
\newcommand{\mathenquote}[1]{\enquote{$#1$\kern.3ex}}

\begin{document}
% upright versions:
``$R$'' is equal to  $``R"$ 

% italic versions:
\textit{``$R$''} is equal to \textit{``R''}

% possible corrections for both versions
\textit{``\/$R$''} ``$R$\kern.3ex''

% recommended approach via custom command and csquotes:
\mathenquote{R}
\mathenquote{a\times b}
\end{document}