I have often seen the term emphasis mine used whenever an author wishes to denote that emphasis in a given quotation originates from said author rather than from the original source.
What is the proper place for this phrase?
One possibility is immediately following the emphatic text, inside the quotation. But, see next question...
What if there are multiple emphatic sections marked within the quote?
If "emphasis mine" comes immediately after each phrase, it would end up repeated two or more times, which seems a bit messy. In this case, would it be OK to place "emphasis mine" at the end of the quotation? If so, should it be inside or outside?
How should the phrase "emphasis mine" be set off?
I believe I have seen parentheses () or brackets , though brackets are also used to indicate words added by the one using the quotation.