1993, John E. Traister, Illustrated Dictionary for Building Construction, Fairmont Press, →ISBN, Mechanical Graphic Symbols, page 372:
WC Water Closet
2015 July 2, “A new symbol for the toilet”, in BBC News[5]:
Here PC stands for "public convenience", according to maps created by Ordnance Survey (OS), the UK's official mapping agency. Not WC, meaning "water closet", widely in use in cafes, bars, restaurants and so on to denote a toilet.