From the NY Times:
So why doesn’t the city crack down on the companies that put up the signs? It is illegal, after all, to post advertisements on public property in New York, and the companies’ phone numbers are printed on the posters.
But as Ms. Brewer said wryly, “We’ve got a little mystery.”
The problem, according to Ms. Brewer, is that the phone numbers are not for the moving companies, but for what she described as referral agencies, mysterious middlemen who collect customers’ information and pass it along anonymously to legitimate movers.