Prison Architect actually received a notice about this. Their answer was very simple: replace the red cross with a green one. There is no reason other games cannot also make this very minor concession to the Geneva Conventions. It is the law.
Look to TV shows. It is very very rare to see an actual red cross. Ambulances on shows like Scrubs don't use them. Film/TV people know to respect that symbol and only use it in very specific scenarios. MASH used it extensively, but then too very carefully.