In the BBC series Doctor Who, the Doctor travels in a time machine called the TARDIS. It is meant to change its appearance to blend in wherever it lands. Its “chameleon circuit” broke before the first episode, so it stays stuck in the shape of an old London police box. Attempts to repair it in later episodes fail.
In 1996, the BBC applied to register the police box as a trademark. The Metropolitan Police challenged the application, but in 2002 the Patent Office ruled in favor of the BBC.