Using masking tape, secure each carton to the other, as shown in the picture. Make sure to leave the egg carton with the flap on the outside.
Punch two holes in the flap approximately 4" apart.
Tie a knot on one end of your ribbon, yarn, or string big enough so it will not be pulled through the hole. Pull string though hole leaving the knot on the backside. Pull the end of the string through the second hole and tie a knot.
If you want to make your bulletin board fancy you can paint it, add glitter to it, or decorate it any other way you desire.
Find some tacks and pictures and pin them to your new recycled bulletin board!