A device for securing a sign to a mullion is provided. The device includes first and second body portions, and a tensioner operatively uniting same. The first body portion is characterized by adjacent mullion receiving elements and a sign support structure. A first mullion receiving element includes a substantially planar member receivable adjacent a mullion face. A second mullion receiving element extends from the first mullion receiving element for tensioned engagement with a first lateral mullion surface of opposingly paired lateral mullion surfaces adjacent the mullion face. The sign support structure is spaced apart and extends from the first mullion receiving element so as to thereby delimit a channel passing between the sign support structure and the first mullion receiving element. The second device portion is slidingly receivable within the channel of the first device body portion and is characterized by a mullion receiving element for tensioned engagement with a second lateral mullion surface of opposingly paired lateral mullion surfaces adjacent the mullion face. The tensioner is operable to draw the mullion receiving element of the second body portion towards the second mullion receiving element of the first body portion.