William sez, "On August 2, 1978, a landmark decision in Reno Federal Court ruled prostitutes are actually brothel employees and therein lies the SIC coding problem unique to Nevada. My father in law was an economist for the federal bureau of labor statistics. Today he shared with me a document he found in the back of a desk drawer. Apparently the folks in Nevada responsible for categorizing businesses by industry (formerly called the Standard Industrial Classification system, now known as NAICS) weren't sure how to label brothels, which had previously been staffed by independent contractors until such practice had been deemed illegal. Thus a victory for worker rights became a nightmare for the local government officials."
(Thanks, William Ray Yeager!)