Anyone with a half functioning brain can figure out which ones are the taxis. Taxis are not yellow in my country and I would have no issue picking those out. They have the very distinctive sign on the roof that no normal car has. Not even OP was confused by this, they are just complaining on the behalf of some theoretical person who might get confused.
Here in the UK, taxis are normally just normal cars with vinyl stickers on the side. I think many people would associate the sign on the top with being a driving instructor's car