Learn English – Punctuation after “Yes”

The Wikipedia article is excellent here (below, my emphasis);

Sic, in its bracketed form, is most often inserted into quoted or reprinted material in order to indicate meticulous accuracy in reproducing the preceding text despite appearances to the reader of an incorrect or unusual orthography (spelling, punctuation, etc.), grammar, fact or logic.[7][10] Several usage guides recommend that a bracketed sic be used primarily as an aid to the reader, and not as an indicator of disagreement with the source.[7][11]

[7] Bryan A. Garner. "sic." A dictionary of modern legal usage (2nd edition). Oxford University Press US, 2001. ISBN 0-19-514236-5, ISBN 978-0-19-514236-5 (pp.806-807)

[10] "Grammar and Style." USD History Guide for Writing Research Papers. Department of History, University of South Dakota. 6/12/2009

[11] William Coyle and Joe Law (2009). Research Papers. Cengage Learning. p. 72. ISBN 0-547-19081-6.

I agree with this passage, and think '[sic]' can be used to highlight a punctuation error. It should be an actual error though, one that can confuse the reader, not marking a stylistic choice. I think your example asserts a stylistic choice rather than an actual error; at any rate, this 'error' does not actually introduce any substantive ambiguity.

I don't think that any settled and widely accepted rule for handling "namely" exists, which makes the challenge to "prove your claims by including references" rather difficult. The link you provide to Merriam-Webster's Learner's Dictionary is useful because it describes some of the numerous ways that people deal with "namely," including these:

—namely,

—namely [no back punctuation]

, namely,

, namely [no back punctuation]

But that source doesn't account for other possibilities, such as these:

(namely,

(namely [no back punctuation]

; namely,

; namely [no back punctuation]

: namely,

: namely [no back punctuation]

. Namely,

. Namely [no back punctuation]

As the contrasting comments and responses to your question indicate, people have very different preferences for punctuating "namely." I favor the —namely, option, which I like because it establishes a clean break from the wording responsible for the deficiency in identification that the words following "namely" are dedicated to supplying. Nevertheless, I can't claim that my preference is anything more than a preference.