This article is a sex guide in Hong Kong.
Under Yau Ma Tei, it lists Portland Street.
"How do you find these brothels? Well here are some pictures to give you an idea. Just look for a sign that looks like this (or similar) and walk right in. The area in which most of these brothels are located are on Portland Street and Shanghai Street with a few scattered further out."
http://singlemansparadise.com/mongering-in-hong-kong-a-beginners-guide/