Q. Do I need a comma before the quoted words in any of the following? (1) She was wearing a T-shirt that said “Girls Rock.” (2) That was team-speak for “Get out of my way!” (3) I came up with “Why would we do that?”
A. Your examples work best as is (without commas). Because they don’t quite count as conventional dialogue (the kind that’s typically found in novels and stories and other works with quoted speech or text), your sentences can incorporate the quotes as if they were simply nouns.
In your first example, the quotation is the object of the verb said; in the second and third, the quotations are the objects of the prepositions for and with, respectively. (You can substitute the word something for each of the quotations to see that commas are unneeded.)
Compare your examples with these: (1) She said, “Girls rock,” which is also what her T-shirt said. (2) The goalie yelled, “Get out of my way!”—though not in so many words. (3) I came up with this: “Why would we do that?” The commas in the first two examples aren’t entirely logical (the quotations still function as objects), but the syntax follows that of conventional dialogue, where commas are normally expected. In the third example, the colon correctly follows an independent clause.
For more details and examples, see CMOS 12.13–17. For the use of the colon in the third example (which would be contrary to Chicago style in your version), see 6.71.