Just my two cents…
As for the British police box, you’re right that they were very common until the 1960’s, but now people only know the police box as the TARDIS exterior. The “context” argument is correct: if you’re making an image of British police in the 1950’s with the police box, then you’ll probably be fine. If you put the police box on another planet, then it’s safe you assume you’re making a sci-fi scene and the model now represents the TARDIS.
However, you also need to be aware of overzealous companies and marketplace websites. I won’t mention the site’s name, but the initials are T.S.
Because they’ve been hit with numerous copyright notices, they are beyond overzealous about what words they allow in their product description. Here are some examples that I’ve had to deal with, simply because (that site) is now so afraid of the copyright holders that they won’t allow any similar words, no matter the context.
Example 1: I upload an F-14 aircraft model for sale and part of the description said something like “This aircraft was deployed on the carrier USS Enterprise.” The site wouldn’t allow that because they said CBS/ Paramount owns the word “Enterprise”, even when it applies to an aircraft carrier or selling an airplane model.
Example 2: I uploaded another aircraft model and the description said something like “The engine intake fed the fuel…” I got a notice that the word “fed” was copyrighted and couldn’t be used in the description!
Example 3, 4, 5, etc: I can’t use the company name in the historical information section of product description, such as “First developed by Boeing, this aircraft…” or “Made in the Mercedes Benz factories, this car…”
So, my point would just be to be careful with copyrighted properties.
Of course, these issues can be avoided if you make your own models from scratch. For example, why does your hero need to look like Nightwing?