This might turn out to be something else entirely, but the following Twitter post from Arrow Exec Producer Marc Guggenheim has led to speculation that The Questionmight be on his way to Star City. The banner outlines a new building development initiative sponsored by WWB/World Wide Broadcasting, which some fans believe could turn out to be The CW's take on Sage's place of work in the comics, KBEL.
Of course, this isn't the first time Hub City has been referenced or even visited on the show, and The Question isn't the only DC character that's based there (there's also Ted Kord/The Blue Beetle, for example) - but Guggenheim is clearly alluding to something relating to this location in an upcoming episode, so it's definitely one possibility.