The IP address indicates.that peand is in Denmark. Although the term WC is not used and generally unknown in America, if you are going to use words rather than jutfrank's suggested picture, I recommend using both toilet and WC. In my opinion restroom is a euphemism and a rather stupid one at that.
I imagine 'restroom' is the more common term in AmE. Either that or 'bathroom'
It might be regional, but you rarely hear or see 'toilet' in my part of the US. It's either 'restroom', 'bathroom', or men's/ladies' room, depending upon who's asking.