Grammatically Correct: The writer's essential guide to punctuation ...

PUNCTUATION
words italics mine, italics added or emphasis added, in brackets.
For an illustration of this, see "Underscoring a Point in a Quote"
under "Italics" on page 284.
Under some circumstances, it may suit your purposes better to
follow the text with an explicit comment in brackets; obviously,
however, this is more intrusive. Other times, it will be best to
simply present the entire quote in an uninterrupted way and have
your comments follow.
• If a quotation contains a misspelling, misused word or factual
error, you may want to make it clear to your readers that it's not
your slip. The convention is to follow the offending text with the
Latin word sic, which means "thus" or "so" (essentially, this is
saying it appeared thus in the original-I didn't mistranscribe it!).
Traditionally, this word is italicized and enclosed in brackets, although
one sometimes sees it appear in roman type and/or in
parentheses. It is always in lowercase.
In his statement, the education minister said: "Grammar standards in our
schools today is [sic] slipping sadly, and I intend to do something about
this."
The time is immanent [sic] for a popular uprising.
He won great acclaim in the Battle of Britain in 1941 [sic], and after the
war went on to a distinguished political career.
You may sometimes want to put sic after an unusual term or
spelling that was used deliberately, in order to assure readers that
the nonstandard word isn't a typo.
The band's new album, Total Waist of Time [sic], contains little that is
original.
Usually, however, such exceptions will speak for themselves.
The advantage of sic is that it provides a relatively unobtrusive
way of pointing out errors. However, it must be used with discretion;
applying it too enthusiastically can make you look overly earnest or
even obnoxious. Don't stoop to adding it just to get in a little jab at an
author's ignorance or to draw attention to errors that are irrelevant or
trivial. If the error is a misspelling, it may be best to just quietly fix
it, unless the blooper is somehow relevant. If the quote is from a
169