Here is the email I received from a GM on this issue a while back when I got mine:
Greetings,
Your e-mail has sparked some debate here, and we have taken it as far as the managers meeting to try to get a reasonable ruling on Portable Ballot boxes.
It was determined that because they do not offer a game advantage (like a portable forge might), then we will not take action on the Portable Ballot boxes. If you would like to purchase it, you are free to do so and display it however you like.
We do appreciate you bringing this to our attention, as they were considered against the rules to own, but because they are fairly benign, we will not remove them from the game.