Here's a video of it in action.
Step 1: Materials
Something that doesn't look out of place on the poster (I used a trading card)
Step 3: Cut Poster
Step 4: Add Back Guard
Tape one of the quarter pieces over the slit on the back. Only tape one side for now.
Step 6: Cut
Step 7: Tape Again
This ensures that your item comes out smoothly.
Step 8: Wrap it Up...
Make a slit about an inch from the bottom of the cardstock, but make it so that only the middle third can be in it.
Once you have done that, Put the middle third into the slit. It needs to stick out about an inch.