What kind of dash is used before a quote attribution?

Question

In this quote example:

“Planning your video is the first step.” -Christine Cloud, Producer

Should the name be preceded by an em dash, or a swung dash?

Answer 1

I shouldn't use swung dash (~) at all.

According to grammarbook.com, the Em Dash should be preferable for a more informal writing in English language. The Em Dash is used (among other cases) to separate phrases.

In any case, I'd rather use:

“Planning your video is the first step.” Christine Cloud, Producer

but this could also be chosen:

“Planning your video is the first step.” —Christine Cloud, Producer

Answer 2

A look inside manmac.tex, which is some macros for The famous TeXbook, reveals the definition of \author:

\def\author#1(#2){\smallskip\noindent\rm--- #1\unskip\enspace(#2)}

which uses --- (EM-Dash) for quotes.