Found this in a guidebook I picked up in an Amsterdam hostel a few years ago:
Prostitutes. If you visit one of the women, we would like to remind you, they are not always women. Do not take pictures of the women. Out on the streets, do not shout or use bad language towards these women. Show some respect. If you have any problems with a girl or a pimp, do not hesitate to ask a police officer. We know why you are there and you can hardly surprise us. So have fun, enjoy our city, and respect this neighbourhood.
just as well to know, I guess!