Restrooms are not for Rest

I remember my first week in the states. It was a small town in South Carolina, over 100 degrees outside and I was walking with my friend when we noticed this sign outside a restaurant:

via

We both were puzzled because:
a. why would a restaurant have rooms for rest? and
b. why would they have to warn everyone that you have to be a customer to rest in those rooms?
I know, I sound silly now. But I swear these were our thoughts. 


For all those years I've been learning English by British books, the "rooms for rest" were referred to as W.C. , toilets or lavatories, but never ever did anyone tell me before I came to America that they are called "Restrooms" or "Bathrooms".

p.s. Did you know that in Canada they name them "washrooms"? Oh the beauty of living and learning! 

I'm telling ya, it's fun to be a foreigner :)