Place one of the pieces of poster board on a flat surface.
Line up the second piece of poster board so that one of its long edges lies flush with one of the long edges of the first board.
Place a piece of duct tape along the entire seam between the two boards and cut off the excess.
Fold the two posterboards together, so the tape is sitting in between them.
Place a 10-inch strip of tape on one side of the seamed long edge and fold it from one poster board to another, an inch from the side, to reinforce the inside tape. Repeat this with the other side.
Place a long strip of black tape along the outside of the taped seam to finish it. Cut off the excess and press it firmly on to the posterboards.
Cut a small hole through both the poster boards one inch below the top of the board, opposite from the taped edge, and 10 inches from the side. Repeat this from the other side. These will be the holes for the handles.
Thread one end of the ribbon into one of the holes in one of the poster boards, looping the end back up to the top of the board and knotting it. Repeat this with the other hole on the same poster board and tie it as well, creating a handle. Do this on the other poster board with the other piece of ribbon to create a handle.