For those newer to Hong Kong mongering, there used to be tons of "yellow sign" brothels in Mong Kok and Prince Edward. There were easily over thirty such establishments. It got its name from yellow signs (sometimes pink) posted at entrances. Here are two photos:
https://ibb.co/FXX19Nb
https://ibb.co/SB9Mb2P
You go up a flight of dark grimy stairs and enter an establishment where a guy greets you. Although he's likely in a triad, those guys are always very polite.
He'll usher you into a small room and ask for your preference.
Then you wait about 3-5 minutes and some lady comes in. If she's not your type, you can send her away and the guy will bring another.
The girls are often pretty good looking. But where these brothels shine is the service. Almost without exception, the service is superb. It's obvious the pimps demand this of the ladies as condition of working there.
On one of my first visits, I said to the guy that I'd like a girl who does BBBJCIM. He looked at me funny and said "they'll do whatever you want".
After you do the deed, you go outside and pay.
Sadly, with the rise of phone apps a decade ago, these places started to die. It seems pimps prefer using hotel reservations instead of wasting time on fixed location brothels.
I've had great memories in these brothels. Now, there are only a few left. None of them have colorful signs in front. The only signs look like this:
https://ibb.co/4jfyKLr
The last time I entered one was two years ago at the height of the pandemic. I remember having to scan the QR code using the Leave Home Safe app. The girl he brought in was hella fat. I have a feeling good looking girls are now rare in these places.