Vernier DTS Flag
This "flag" is designed to increase the end profile of a Vernier dynamics cart for use with a sonic motion detector. Vernier sells a flag for $6 dollars that somehow is held on by magnets. Have not purchased one or seen one in action, but I figured it would be easy enough to make a flag that mounts to the top of the cart.
Print time at medium speed and 35% fill is about 1 hr. My print fits pretty snug so for me the bolt is probably optional, but your print may vary. As shown, I have used Vernier mounting hardware I had lying around.