In the U.S., "bathroom" would work in all of these situations in conversation. Oddly, I don't think we actually use the word "bathroom" on a sign, but everyone would understand "bathroom" and would direct you to the right place.A very interesting discussion indeed. As a non-native I have found all this information very interesting and sometimes slightly weird as, for example, the usage of "restroom", "washroom" and "bathroom" more common in AE. However, I would like to summarize all the points of view expressed so far so as to know exactly particular names of "toilet" in different places. Below I have written the list of places where toilest definitely exist. Please, point out how it (toliet) is usually called there:
1) at schools, universities, colleges, offices (at work)
2) in public places (at railway stations, at hospitals, in supermarkets, in the street)
3) in cultural public places (at the cinemas, theatres)
4) in some means of transport (on the trains, on the planes, on the intercity buses)
5) At home
On a map or guide you would most likely see the word "restroom". This is also a common word on signs. In all situations except a home, "restroom" would be a polite word to use. I have heard people use "restroom" in homes but it strikes me as a little odd. I think of a restroom as a public facility.
I can't imagine seeing "WC" or "toilet" on a sign in the U.S. I believe "lavatory" is used on planes.
 I'm sorry. I missed the additional informaion about the question. The sign directing you to the location of the rooms would say "restroom", but for the actual sign on the door, I would expect to see the international symbols in any public place and the word "men" under the symbol for a man and "women" for the word under the symbol for a woman.
I haven't read through the entire thread carefully so I may be repeating someone else, but in the U.S. "toilet" brings to mind the actual fixture you sit on, not the whole room.