zlacker

Right. There are several less well known protective marks, all red symbols on a white background. There's a red crescent, and a red crystal (an uncontroversial geometric shape which conveniently is also hollow so you can put some other symbol in there if that's important to you) and historically a red lion with sun.

The purpose of these symbols is to unambiguously identify protected vehicles, protected buildings, protected people.

It's true that in some countries people slap red crosses (in particular) on stuff that shouldn't have them and doesn't need them. But that doesn't make it a good idea. In a video game in particular you could use any symbol and players would soon get the idea. How long do you think it takes Mario players to realise that one of the mushrooms makes Mario bigger, while a different one is an extra life?