I used cardboard for this project, but you could use a poster board if you want. Make sure the cardboard is thin enough to fit the servo through. I also used markers to make the sign and scissors to cut out the arrow. Tape is good for holding everything together.
Attach the Arduino bit to your computer and upload the code provided. This is a simple button code I found on the littleBits website.
Assemble the litleBits
Look at the picture and assemble the bits and place them on the mounting board.
Attach to your sign
You will need to test the servo to see where it turns so that you can align the arrow and the servo so it points the correct way each time you hit the button. Once you have the servo lined up, attach the servo to the back of the sign and you are all set. Push the button and the watch the sign switch back and forth. The button is sensitive, so if you hold it down too long, it will bounce back to where it started.