"Non-Commercial Use" of Commercial Properties
I have long understood "non-commercial use only" to forbid making money directly with the product in question or renders thereof. And sometimes the reason for this is that the models represent other parties' commercial properties (Batman, X-Men, Doctor Who, et cetera...). But what if my character is just a London Bobby of the early 20th C. and has good professional reasons to use a perfectly ordinary blue police box? Or the mask my hero fights the Astral Syndicate in is cut to the same pattern as Nightwing's? At what point does the line between infringement and fair use generally get drawn?