My point is that regulation won't work, as most women will simply not register with local authorities. What benefit does this give them? A public record as a prostitute? The link I provided gives reasons why this is undesirable.
Aside from a few hardcore libertines, most women don't get into prostitution because that's the profession they want. Usually they are exploited by men or become desperate for money and seek income in the only guaranteed way of which they can think. Street prostitution, at least in the U.S., is reserved now for mostly desperate/ignorant prostitutes, as internet boards in the form of Craigslist ads and other places have replaced more random types of meetups. I was watching a show about pimping the other day that explicitly stated that prospects for pimps are dwindling as a result of the internet, since women need no intermediary to locate clients for them.
For harm reduction, the only thing I can think that would work is full decriminalization, sans regulation. I think that clinics and other help centers would spring up naturally as a result.
Trafficking and underage prostitution should still, of course, be totally illegal. Pimping and pandering another person for prostitution, similarly, would remain illegal. In my decriminalization scheme, internet sites would gain an exemption from pimping and pandering laws in case some group wanted to argue that, say, Craigslist, was de facto pandering for sex services